Sega Genesis Shoot' em Ups!

The Sega Genesis/Mega Drive is known for its for shooters.  There are A LOT of shooters on the Genesis, so much so that I don't have the stamina nor inclination to write about them all. I should mention that I don't consider games like Contra Hard Corps or Gunstar Heroes as shoot'em ups, I consider those their own genre (Run'n Gun). Also, Games like Desert Strike and Herzong Zwei are more like strategy games than shoot' em ups. These are the games that I own, loosely ranked from least favorite to awesome.  Here goes...

Xenon 2
This game prioritizes graphics over gamespeed in the worst kind of way. From afar it looks like it has potential, but the chuggy speed feels like a flipbook. Maybe you should just look at pictures of this game instead of playing it.

Battle Squadron
This is a port of the Amiga game, which was apparently a better version. The gameplay speed is fine, and the visuals are passable if a bit generic, but the thing keeping this game down is the fact that all enemies are bullet sponges. Mini bosses and end bosses are expected to be fairly hearty, but the opening slavo popcorn enemies? 

Bioship Paladdin
This game is unique in the genre, in that your must control not only your ship but the aiming reticle as well. In a genre of one-hit deaths, your vessel is relatively tank-like, and it will have to be since your attention is divided between both actions. 

Heavy Nova
A port of the Taito arcade game, this home version is fairly faithful to its progenitor, but is a bit heavy on the memorization. 

Cross Fire
Do you like variety in your shooters? How about mixing a shooter with a run'n gun? This game was originally going to be an Airwolf game, based on the 80's TV show. Stages alternate from overhead vertical shooter to ground based run'n gun. It does both, but neither parts are special. 

Red Zone
Speaking of mixed genre games, Red Zone is another hybrid game that tries to combine both gameplay types. Released late in the Genesis life span, this game is notable for some impressive advanced graphics, such as the opening cinematic, and the overhead psuedo-3D stages. It's too bad that it is form over function, as the controls and hit detection leave a lot to be desired. Maybe it is by design, but the helicopter control is very laggy and drifty, and not fun. 

Rescue me! but don't crash and kill us all!
This game has an interesting concept: pilot a craft in and underground cave system, and rescue people. This is a borderline shoot' em up,its kinda like Choplifter underground. Your focus is extraction. The problem is, the game has physics. Like, somewhat real physics. Momentum is not your friend when you are trying to navigate a craft through crevices and underground caves, especially when your craft has the durability of a Faberge egg. I thought I was patient with hard games, but this one I almost threw across the room. People more willing than me will enjoy playing it. I you love really games that are hard due to controls, try this.

Space Invaders '91
This is an update of the classic game that is said to be the first shoot'em up. It retains the same spirit and gameplay of the original, with faster speed and music. Instead of having fixed shields to hide behind, you now have a shield with hit points. It's a basic game that has its moments. There's not much more to say about this. 

Super Thunder Blade
I loved this game in the arcade. You sat in the cockpit, and handled the yoke with fire buttons as well as a thrust shifter. The sprite scaling mechanic was brand new, and it blew everyone away. The movement of the screen and seat conveyed a somewhat realistic sense of physics. When this was ported, it quickly became apparent that what worked in the arcade did not work at home. Your helicopter moves too slow on screen, and the enemy bullets, which up scale as they head towards you, are too large, leaving you little room to survive. Add in the environmental hazards like buildings, trees, caves, etc, and you have one unnecessarily hard game. This is perhaps an instance where the game should have been rebuilt from the ground up for a home port, instead of trying to force a unique arcade experience into a cartridge. Off topic, but I'm glad Sega ended their brief use of "Super" in the titles of their early games. I bought it for nostalgia, and there it shall remain. 

Air Diver
What does this button do? And this one? And this one?
So this game wants to be After Burner II, but there are problems. Nearly half of the screen is your cockpit, which is crazy-busy to the point of distraction. The remaining play field is so small, that enemies need to be small. When they're this small, they're hard to target and shoot at. They don't seem to have the same problem aiming at you, so gameplay suffers. I understand that the Genesis perhaps could not handle an entire screen of action with sprite scaling, but wait, oh yeah other games managed it. This is a clunker.

Atomic Robo-Kid
Meet Atomic Robo-kid, your favorite flying robotic garbage can.

Here is a different horizontal scroller where you are a stout robot that walks or flies, almost a hybrid of a run'n gun and flying shoot'em up. The visuals are bright and creative, but your protagonist is the least appealing sprite on the screen. Some my find it charming, but all I see is a walking garbage can with a rocket pack. The gameplay is just OK. 'The corridors don't offer a lot of space, and your sprite is so large, so you need some impressive maneuvering skills just to get through the first level. There are variable power ups that you can pick up, but I don't find them that helpful. 

Darwin 4081
Quick, grab the DNA!

This is another Japanese exclusive. It is a vertically scrolling shooter, with a forward shot on the A button and a ground bomb attack on the B button. The game has an interesting concept: collect the DNA of defeated enemies and mutate your ship. Your ship will visibly change and new powers will be obtained. The problem is, you have no idea what DNA does what, and get shot down when you're trying to collect the DNA. When you respawn, your ship devolves one level, which is better than starting from scratch. The graphics are ok, but every shape the ship morphs into just looks like a squid face. The music is blah. Maybe the game gets better, but I never feel like continuing further to find out. 

Grind Stormer
Face the wrath of Mike & Ike candies!

Do you know when you play a handheld game that is emulated on a larger screen, the look of blown up pixels due to magnification? This game is like a game gear game with a resolution of 120 pixels, blown up to fit a standard TV screen, giving it an 8-bit look even though its a Genesis game. Everything is larger on screen: your ship, enemies, bullets, etc. The enemy bullets, which look like Mike & Ike candies, fling towards you and are huge, they are about a quarter of the size of your ship, increasing the difficulty right there. My guess is that when this was ported, the developers decided zoom in on the bottom half of the play field, rather than reprogram. There's just not enough room/time to react when enemies appear. Also, being a Toaplan game, with its old school, merciless game design, it is too hard to enjoy. 

Final Zone
Not entirely a pure shoot'em up, this game could be seen as a run'n gun, as your mech is on the ground walking/running. The game uses an isometric viewpoint, and plays better than most games that have it. There are a predetermined number of each enemy type that you have to dispatch in each zone. Your fire is locked in the direction you are facing, until you release the fire button. You can equip different weapons on different parts of your mech, introducing some strategy in taking out different types of enemies.  You have a life bar, which seems generous at first, but your mech is fairly wide, and your movements are mostly restricted to the streets in-between buildings, so it is hard to avoid bullets. The game is oddly enjoyable, if a bit rough around the edges. In what is kind of a dick move, you do not get your health bar replenished after beating a level. There seem to be unlimited continues, however.

Space Harrier 2
This is an on-rails type of shooter, with simulated 3D through sprite scaling. The original Space Harrier was a revelation. Yu Suzuki's masterpiece will go down in history as one of the most iconic Sega arcade games of all time. This follow up feels like it was made to cash in on that legacy, but it pales in comparison. While the core gameplay is identical, all of the details fall short. The visuals are OK, the music is meh, the gameplay and fun factor are all disappointing. There is nothing outright bad about the game, and It might be a cool game to someone unfamiliar with its predecessor, but to those who spent hours playing the original, it doesn't compare. It's a classic case of having too big shoes to fill.

Dangerous Seed
A simple vertical scroller, that comes across as rudimentary. The enemy design is odd and the background visuals are ok. The music is above average. Every enemy takes several hits to destroy, and so there is always a crowd of them on screen. Initially, the power ups are not powerful enough to make up for the deficit but you can upgrade them as you progress and things even out a bit. There are different weapon configurations that are toggled for different weapon fire patterns, adding to variety in the gameplay.  It took me a few play throughs to appreciate it, and I can appreciate it better now. This game was only released in Japan.

Twin Hawk
An early Toaplan arcade conversion, Twin Hawk is a history lesson of the banality of early vertical shooters. The pace is glacial, and enemies grounded, as in, there are no flying enemies. Your weapon is a basic vulcan, and is not all that impressive. Your bomb attack is a flying squadron that takes fire for you and shoots straight ahead. This is short lived, as they are easy targets with large hit boxes. There's nothing wrong with Twin Hawk, but nothing that impresses either. It's a basic entry level shooter. It is hard, but that's to be expected from Toaplan. It was only released in Japan and Europe.

A vertical scroller, this game looks good, with lots of parallax scrolling. The sprite design is fine, if a little generic. The music is good, probably its best feature, and the developers knew it; the music plays while the game is paused. The gameplay is reminiscent of Toaplan, in that large sprite/hitbox way. It is fast paced, and the action constantly keeps you on your toes. Overall, it's a good game. Except maybe starting the stage over when you die, that sucks.

Panorama Cotton
The Cotton Series started out as a horizonally scrolling cute'em up, and has versions on the PC-Engine CD and Super Famicom. This Mega Drive outing is a sprite scaling rail shooter. I understand the appeal of these games, but I don't enjoy them that much. Maybe its because the frame rate doesn't seem high enough for a convincing sense of 3D movement, or the stuttering progress of the screen is unpleasant. I understand the limitations of hardware at the time, but I don't feel that these games hold up today. As for this game in partucular, it has the cotton tropes of collecting crystals for power ups, cute voice samples, and uber-bright visuals. If you like games where you fly into the screen, check it out.

Galaxy Force II
This is a highly amibitious port of the arcade hit, and the it't pretty well done. The control is what you expect from a Sega sprite scaler from the early '90s. I've never really been a fan of the energy count down mechanic, so it set it easy and its less stressful. The game looks great, and its one of the better almost-3D games on the system.

After Burner II
Another sprite scaler, After Burner was a monster hit in the arcade. It was known for its cockpit seat, which rotated and turned with your movement on the stick. There was stereo surround sound, and the music was hard rock, not unlike Kenny Loggins' Top Gun song. The action was fast and furious, and enemy counts are sky high. The Genesis port is an admirable take on the source material, keeping in mind the hardware limitations. Sure, there are less detailed backgrounds, and fewer animations, but the essence of the game is still here. It gets hard, as the sprite scaling can play tricks on your sense of depth, especial when it comes to enemy missiles that are partially obscured by the view of your ship. Again, these are issues with this type of game, but AB2 has some strong nostalgia for me as it was one of the first Genesis games that i owned. 

When G-Loc was released, it was puzzling that Sega would put out a game so similar to After Burner II. This game takes notes from AB2, but does so at a less hectic pace. The gameplay is similar and intuitive, so anyone can pick up and play. It's perhaps more playable as the pace is slower, and you can be more methodical in how you pilot your plane and fire on targets, whereas in AB2 you often resort to spastically flailing around from corner to corner to avoid droves of enemy fire. The different pace is welcome, resulting in an underrated game.

Burning Force
Burning Force is a vehicular pseudo 3D shooter with vivid colors. It is clearly inspired by Space Harrier, but has its own ideas, like upgrading you vehicle as you progress in the game. There are a couple of different weapons to pick up. It tends to be a bit on the easy side, as enemy shots make a particular sound, tipping you off when to look for them. The wide shot takes care of a large portion of the screen, really reducing the challenge. Still, its a fun game, with slightly different gameplay.

Arrow Flash
Early horizontal shooter, where your ship can transform into a mech at any time. The mech looks like a cute robo-teddy bear with a big blue belly. The ship is more nimble, and a smaller target, and the mech is larger and slower. If you have picked up an option, it trails your ship's movements, but in mech mode it aligns to a set position relative to the mech. Other than that, I'm not sure what other difference there is between modes. You have a super attack called the "arrow flash", in which you turn into an invincible energy ball until the attack timer runs out (extra bars of time can be picked up). It's pretty useful for boss battles. The visuals are about average, and the music is unremarkable. It is an easier game on the system, due to the enemy bullets being huge and flashing. The controls are tight, and overall its an enjoyable game.

Insector X
That's one tricked-out hornet
A horizontal scroller where you are an insect-man, flying to the right taking out all sorts of bugs and insects that are armed. This does have some interesting graphics and is a nice change of pace. Your humanoid is easy to control, and deaths are usually your fault, however I find that the smallest enemies are the most difficult, due to their fast movement and speed changes. The bosses are predictably larger insects, armed with machine guns. It's a little absurd, but it's fun. The music is not bad. The backgrounds are a bit static, with a noticeable lack of parallax scrolling. It's a game that's easy to pass over if you look too quickly. 

Air Buster
I hate these tunnel stages
This is fast-paced horizontal shooter, also ported to the PC-Engine. It's fairly straight forward, with different power ups that can be picked up. The manner in which power ups are given is unique, in that when the power up carrier is shot, five or six power ups spring out simultaneously, and you have to think fast as to which one you want and which one you can get to before they fall off the screen. 
Your shot is single shot or rapid. If you hold the single shot you can charge up a flash attack, which damages all enemies on screen. It has potential, but it didn't seem worth the diversion as you are defenseless while charging. The game has this gimmick where the scrolling speeds up, and the passage narrows. Obviously you have to maneuver through it without crashing. While it adds to the variety, it gets hold quick. Your death animation is a cool smoke-trailing descent. Overall, its not bad but its not great.

Also released for the Sega CD as Sol Feace, Sol Deace is a horizontally scrolling shooter. The visuals are nice, and the screen can scroll up and down about 10%, which doesn't do that much, but it gives the game a greater sense of space. Your first power up is a set of gattling guns that affix to the top and bottom of your ship. They animate with a recoil when shots are fired, and they can be locked in at different firing angles, which is a nice touch. The music is an upbeat jazz, like you'r find in a tropical island resort in the 90's. It's a decent game. The Sega CD version is nearly identical, except for the CD streaming music.

Bio Hazard Battle
This is a biologically-themed horizontal scroller, where you pilot a creature of some sort, maybe skates or rays? The enemy designs are cool representations of realistic and fictitious creatures, and they are well drawn. Your primary shot varies, depending on which creature you select. Holding down the single fire button releases a charge shot, which is helpful during boss battles. You are equipped with an option, and its direction of fire is reverse from which direction you are facing. This adds a small amount of interest in how you position yourself to fire at enemies. Also, the weapon pick ups vary from lasers, spread shots, rings, etc. The graphical design is different and interesting. The music is odd, but matches the theme of the game. 

Your tank is oddly nimble in tight spaces
This a ground-based game where you pilot a tank, or "Granada", and have to navigate a map to take out enemy emplacements. Your fire is free aiming, and by holding the B button you can lock your direction of fire and strafe, which is very necessary. Your sprite is relatively small, and this is done to emphasize the scope of the play field, which is huge. Your tank is really fast and agile, and control is spot on. It's a good game that reminds me of Jackal on the NES, only less linear. Definitely worth picking up. 

Twin Cobra
Hey guys, thanks for painting the tanks neon orange!
From afar, this looks like a generic shooter with generic power ups and typical gameplay.  Actually, up close that's what it is, but it does it well.  It is a no-frills, simple, straight forward, helicopter shooter.  I'm not sure why I like this game, but I do, and I am pleasantly surprised every time.  Maybe its because it plays just like you expect it to.  Maybe its the pick-up-and-play simplicity. This is a Toaplan game, so expect it to be hard.

I don't know why Medusa likes to throw bacon around
You play as Apollo, on a flying pegasus, out to rescue Princess Artemis. Given the mythological theme, various expected players make appearances, like Medusa. 
You charge your sword shot by holding the fire button, this is fairly effective against enemies directly in front of you. Options and other power ups can be picked up. You can withstand up to four shots before your life is lost, which feels like the right amount. It's a fun game with interesting enemies.

Whip Rush
There's some great depth in the backgrounds
A straightforward but solid horizontal scroller from Renovation, Whip Rush doesn't get too ambition with its game design. Your ship, which is shaped more like a pod, is small and has variable speed that is selectable with the A button. The level design makes use of this, as there are clearly times where slower speed is advantageous, and other times your need to move fast. Power ups are interesting, as they are accompanied by an option, which can be placed in different positions relative to your ship. Again, the direction of fire is variable, as the screen scrolls vertically as well in some stages, and so being able to fire downward is useful. The graphics are on par for the early Genesis years, and the music is fine. The control is tight, thanks to the variable speed. This is an underrated game.

Super Fantasy Zone 
Is there some kind of message in the background?
This was the earliest cute'em up that I can remember. The colors and graphics are so bright and appealing, its really drew kids in just to kick them in the teeth with some hardcore difficulty. Besides that, it's a really fun game. Too bad it wasn't released in North America. One of the main features of this game is collecting money to spend on power ups in the shop. You can purchase upgraded weapons, but the price increases each time you buy the same item. This sucks, but I suppose it adds some strategy as far as when you buy which weapon. The option for rapid fire is appreciated, as this was release in a time when that wasn't a given. 

Sagaia (Darius II)
This is the first Darius game released on a Sega console as far as I know. This first entry was oddly named differently than the series. On other consoles, it was named as Darius II. Sega couldn't help but mess up in the 90's on the simplest decisions. Anyway, this is a solid rendition of the arcade game. The game has been zoomed in from its original 3-screen-wide format, and its plays fine. The graphics perhaps take a hit as the sprite designs seem as if they were designed to be viewed when zoomed out; I'm not sure about that, it's just my impression. As with all darius games, branching paths are available after each stage, adding to replay value. Uniques to this version is the ability to play with the Red or Blue ship. It's a challenging, yet worthwhile game overall.

Robo Aleste
Can't. Slow. Down.
When I heard that this game was the sequel to the outstanding MUSHA, I made it a priority to obtain. Unfortunately, it doesn't have the same vibe as MUSHA when it comes to gameplay. It's a lot more difficult, for various reasons. For starters, all of the enemies take multiple hits. I know at the beginning of the game, your pea-shooter is generally weak, but couple that with waves of enemies that take several shots to kill, and you invariably have a screen full of enemies attacking you. Second, it seems most of the enemies come at you from behind. Again, this happens in a lot of other good games, but it is overused early and often in this game. The mechanic of repositioning your drones is gone. It has some good visuals, if a bit drab in color palette. The backgrounds have interesting graphics, like tiny people wave at you while their village is burning(?). Overall, its not as good as MUSHA, and not much fun.

Zero Wing
Translation winner is you!

"All You're Base Are Belong To Us!!" Now that we got that out of the way, Zero Wing is a horizontal scroller from Toaplan. It is highly stylized, and has some rockin music. Your ship does move pretty slow, and your starting weapon is fairly weak. Speed ups are common, so that's not an issue. The first power up you encounter will provide you with two ship-side options that will triple your firepower, and these come right away after your die, so that's helpful. Your ship also has the ability to capture small enemies and shoot them across the screen, which is pretty fun. I haven't encountered a time where it was necessary, so I wonder if it was an add-on late in development. This is a fun game, with wildly rampant Engrish. It's a must play for die hards.

Task Force Harrier
Too much gray
A vertically scrolling shooter, Task Force Harrier takes elements from other games to add to its own gameplay. Your Harrier jet fires forward, as well as drops bombs slightly ahead of your craft, requiring you to mind both planes of enemy attack. Differently numbered icons will change your bombing pattern, so its fun to experiment which one works best for which stage. Additionally, your options can be positioned in different formations, each of which will be more or less suitable for different scenarios. You do have a big bomb attack, but I found it pretty weak overall, and even forgot to use it (read: I didn't miss it). There are some great voice samples throughout, and the music is decent. The graphical design is the lesser impressive feature of this game, but it doesn't hurt the playability. 

Vapor Trail
Do a barrel roll!
This is a vertical scroller made by Data East. The game has three selectable fighter planes, each with varying speed and power attributes. Your ship has a life bar, in addition to having multiple lives, which is uncommon for a shoot' em up. Various weapon power ups can be had, but a unique feature is the roll attack. Pressing C will cause your ship to turn into a blur, during which you are invulnerable, and can inflict major damage. This needs to recharge after each use. The music is really good, the graphics are nothing special. There are some voice samples, but they all sound like the guy has marbles in his mouth, with the exception of "Vapor Trail" sounding off every time you pause the game. Besides that, it's a great shooter that also boasts 2 player co-op, an uncommon feature at the time.

Battle Mania Daiginjou
Bosses are huge, requiring lots of direction changes
Also known as Trouble Shooter Vintage, this is the sequel to Trouble Shooter. The same core gameplay mechanics are present, which is a good thing. The graphics received an overhaul, and the music is more upbeat. Little tweaks here and there over the first game make it that much better. The charge weapon feels more powerful, there are reflections of the players on glass panels, to name a few improvements. Eight way shooting is available in the options, and it changes the game play, making it harder in my opinion, but some prefer playing it that way. This is just a fine example of horizontal shooter. I can see why it is desirable, but today's asking price is nuts.

Thunder Force II
Always aim for the center
The first console entry for the series, TF2 was a launch title for the Genesis. While the seeds of the series are apparent, there were a few quirks in this game that later entries ironed out. First, the overhead stages are fairly polarizing. The movement during these stages is fast and janky, making collision deaths very real. These were promptly dropped in the follow-up. The weapons were varied if a bit primitive, but the bigger issue was that you lost all collected weapons when you died. The music was serviceable, but the song writing had not matured yet, that would happen in the 3rd and 4th games. Despite it being outshined by its siblings, it is still a good game and fans of the TF3 and TFIV should try it.

A rare horizontal scroller from Toaplan, this game carries with it the traditional Toa-pain. Difficulty aside, the unique weapons make for stimulating gameplay. You can change the direction of your shot by pressing B, and this is necessary to take out the various enemies that placed in various nooks and crannies in the stages. Bosses will have weak spots all over, and so depending on your position you might have to switch to a vertical shot, reverse shot, angel shot, etc. It's inventive enough to keep you coming back.

Elemental Master
Developed by Tecnosoft (of Thunder Force fame) and published by Rennovation, Elemental Master is of the running humanoid variety. Similar to Thunderforce, you can select between acquired power ups. A different mechanic is the ability to shoot forwards and backwards with different buttons. Fans of Thunderforce will pickup on clues here and there that reveal its heritage, like similarities to TF power ups, initial stage select, music style, and certain sound effects. It's a fun game, and a nice hybrid of genres.

Bringing 3D polygons to the Genesis, Sylpheed was an impressive feat for its time. Simple as they may be, the polygons provided enough depth for a convincing 3D environment. The gameplay is fluid, and the music is pretty good. It takes a while to get used to the hitbox of your ship, having that extra dimension, but eventually you'll get the hang of it. This deserves more recognition than it gets, and perhaps might have were it not tied to the Genesis add-on craziness of the mid nineties. 

Forgotten Worlds
This is an interesting shooter that has horizontal and vertical levels, and two player co-op.  Enemies drop "zenny" (money) when destroyed, that you can use to purchase power ups in the shop that pops up here and there.  The control scheme takes some time to get used to, as A rotates your player in one direction, and C rotates the opposite direction.  The stages are typical but the boss designs are inspired.  The music is good, and the sound effects are a little rumbly here and there, but not to a fault.  A lot of fun to be had here, especially if you play with a friend.

Twinkle Tale
You play a little girl with magic projectiles, and you walk the terrain instead of flying. It's a borderline cute'm up, and gameplay is reminiscent of Pocky and Rocky on the SNES. You can pick up 3 different magic attacks, which can be selected on the fly with the C button. There's a concentrated forward firing magic, a homing magic, and a spread magic. Each increases in power when picked up. You also have a screen clearing magic, and there different varieties of that as well. It's a fast moving game, and despite its cutesy appearance can offer a nice challenge. Character sprites lean towards the mythological, with impressive visual style. It was only released in Japan, but there are translated hacks out there, not that you really need them to play the game. It's just a great game that makes you want to keep playing. 

Raiden Trad
A solid port of the arcade, Raiden Trad is important as an early vertically scrolling shooter. It is the epitome of easy to learn, hard to master. There's no gimmicks here, everything is straightforward, and done well. The gameplay is exactly as you'd expect. Two kinds of power ups: the vulcan that spreads when powered up, and the straight-ahead laser that becomes more intense with power ups. The bomb is iconic, its the first of its kind that I remember. Unfortunately, there's no two-player co-op play and the color palate of this port is a bit pale compared to its competitors, but that's reaching for something to complain about.

Trouble Shooter (Battle Mania)
In this horizontally scrolling shooter, you control Madison, a teenage "Trouble Shooter", and her partner, Crystal, in tandem. Flying humanoid shooters have come before, but this one is unique in that you control two characters simultaneously. Madison always fires forward, and you can change the direction that Crystal fires by tapping the C button. Even though you are controlling two figures on screen, the only hit box that you need to worry about is Madison. This takes some getting used to, and eventually you realize that you can use Crystal as a shield. The direction switching mechanic works fairly well, and the gameplay makes good use of it. There is a special weapon that you get outfitted with at the onset of each stage, it acts as your super bomb. There are a few types, and they are reusable after you let it recharge. The music is great, and visuals are about what you'd expect for a mid-life Genesis title.

This is an early release for the Genesis, and that is reflected in its merciless difficulty. Your ship's hitbox is HUGE. Sometimes it feels like it is larger than your actual sprite. Power ups can be had, but they come after picking up 4 "P" icons. This helps level the play field a little, as they significantly increase your offensive power. Three different weapons can be had, but I prefer the standard vulcan as it has a bit of a spread, covering a little more of the screen. Speed ups are necessary, but don't get too many as your giant hitbox will scrap against the hair of an enemy and BAM! The visuals are bright and colorful, and the music is organ-grindey, like a progressive rock band took over a church on a Friday night. It's a fun game, but it takes a lot of pain to get any good at this one.

Steel Empire
In this steam punk inspired horizontal shooter, you can choose between a blimp and a biplane. The blimp is larger and slower, and can take more damage. The biplane is nimble, but less sturdy. Given that this is the only time I've ever seen a blimp as a selectable character, picking it is a no-brainer. The visuals are very distinctive and stylish. Right from the start you are presented with the clicking sound of a 1940's video projector, as it lays out the backstory. The color scheme recalls sepia tones of vintage photography. The music is excellent, and a great example of Genesis sound programming. Your ship can fire to the left or right with different buttons, and this is incorporated into the gameplay design fairly well. The steam punk aesthetic is in high gear, and many of the enemies are inventive almost to a fault (flying windmills and bathtubs?). Your ship does toss bombs, but does so with a bit of an upward arc, which makes aiming at ground targets difficult. Your primary weapon is a basic pea shooter, which can get powered up but is mostly underwhelming. The lighting attack is limited but fierce, so save these for the boss battles. Overall, this is a fantastic game with great design.

Android Assault
There's something about being a game on the CD format that invites guitar wailing butt rock. Android assault is a very good game that is reminiscent of Thunder Force 3 or Gate of Thunder. It's very playable, has great graphics, has adjustable speed elements, and a variety of power ups. It also has a rock'n soundtrack. Your ship transforms into a robot with the third power up, and that makes it all the more awesome. Oddly, Even though the Game is titled Android Assault, the title screen shows The Revenge of Bari-Arm as the title. Oops.
It is a lot of fun to play, but it's a hard game to find. I recommend seeking it out.

Wings of Wor
This is a fresh entry in the shooter genre for the Genesis, as it has a mythological theme. You play as a flying centurion, or something like that, and fly from left to right on the screen. The graphics of the protagonist and common enemies are nothing special, but there are some pretty awesome and grotesque bosses in this game! There are some neat visual effects, like the screen tilting, and lots of prallax scrolling. The music is serviceable. Power ups are fairly plentiful, and you can use various forms of offensive magic that you pick up. This game is a breath of fresh air, and is highly recommended.

Keio Flying Squadron (reproduction)
Keio Flying Squadron is the premier cute-em up on the Sega CD/Genesis. It has great hand-drawn sprites, bright colors, and fluid gameplay. The music is good too. Fans of Parodius will definitely be on board with this, except I feel this is the better game. The difficulty is balanced, and you don't really get frustrated. The enemies are so cute I feel bad blowing them to bits, but that's just the way it is I guess. This game goes for ridiculous asking prices on Ebay, I went the repro route. Find a way to play it, you won't be disappointed. 

These graphics still hold up today
This game has a unique weapon-stealing feature, where you toss you option (the TOZ system) at enemies, which copies their firepower for your use.  This can be done three time in succession to increase the power of your weapon.  No other power ups are provided, and not all weapons are equal.  Its a novel idea, and works well here.  Part of the fun is experimenting to see which enemies provide the best weapons.  The difficulty is rather high on this one, especially with bosses and later stages.  The graphical design is excellent, as stages and bosses have a certain energy to them.  The music is pretty good too.

Eliminate Down
Get used to dodging
This Japan-only release is notorious for its ridiculous asking price.  I sold almost my entire Gamecube collection to fund this purchase, and I don't regret it. It offers meticulously detailed sprites, impressive animations, and lots of action. This game pushes the system to its limits, and would have been a great asset to Sega in the console wars had they released it stateside.  Seriously, you've never seen the Genesis pull off some of these animations before.  The amount of sprites on the screen at once is impressive. You have selectable speed settings, as well as different weapons to toggle through on the fly. These options are nice, and difficult to change when the action gets hectic. Perhaps its difficulty dissuaded Sega from a worldwide release, and it's a shame, because this game could have been a system seller.

Fire Shark
A simple, world-war 1 bi-plane shooter with three available: the spread shot (think Raiden), an figure-8 bullet pattern shot, and the awesome fire stream weapon that when fully powered up lashes fire all over the screen.  This game in not too difficult when maxed out, but dying in the later stages is rough as it is hard to get powered up when it takes all you have just to survive.  Perhaps this is another entry that I am placing higher on my list than the consensus but its just so much fun.

Advanced Busterhawk Gley Lancer 
Best use of options in any 16-bit game, in my opinion
Another Japan-only release that is a shining example of what the Genesis can do with great programming. The game has very striking visuals, it seems that almost every line of resolution has parallax scrolling, The asteroid field in stage 1 is one of the best looking backgrounds of this generation. The unique feature of this game is being able to customize the behavior of your options.  You can have them spin around you, fire in the opposite direction, fire at variable angles, follow you on a string, etc.  There is a choice to suit everyone. Gradius V on the PS2 offers similar option customization, but that came out a decade after this game. The gameplay is tight, difficulty is balanced, and there are interesting vocal samples when power ups are acquired. The music is awesome. All around, a great example of a horizontal shooter.

Lords of Thunder
This is definitely an interesting game. It is a mythological flying humanoid horizontal scroller, with blaring, guitar driven butt-rock. Despite the heavy use of adjectives, it is a stellar game for the Sega CD. Your character can fly or run, when on the ground. If enemies get too close your melee attack is a fierce sword strike. You can choose different types of armor before each stage, each of which has different magic capabilities offensively and defensively. Downed enemies will drop gems, which are used as currency in the shop between stages. This allows for trying a variety of magic and weapons, adding to replay value. One of the best games on the system.

Lightening Force (Thunder Force IV)
The stage colors change as the sun sets
This game widely regarded as the pinnacle of Tecnosoft's (Technosoft (sp?)) flagship series, and it's easy to see why. The graphics are gorgeous and plentiful, the music is sophisticated and energetic, the boss battles are challenging and the iconic weapons are a blast to use. The game modifies your ship halfway through and equips you with an energy blade, which is ridiculously powerful, provided you get close enough to a boss to use it effectively. This is a hard game.  It is enticing enough to keep you coming back, but make no mistake, it's the hardest of the series. It truly does live up to its billing, and the reason I don't have it higher on this list is because the other games have some serious nostalgia going for them.

Position your drones behind you when the walls close in
This game is part of the Aleste series, by developer Compile. Many people, including myself, consider it the best of the series. The graphics are well designed, based on Japanese mythology combined with mecha. The music is heavy and melodic, and the gameplay is superb.  Your main shot can be powered up by collecting dropped p-chips. Collecting these will also build up a collection of drones (options) that can be configured to fire is various directions by pressing A. You can also acquire a secondary weapon (laser, bombs, shield) that can also be powered up by collecting the same icon. Your speed can be adjusted at any moment. This game is so well executed that it receives nearly unanimous acclaim. Considering that it was an early title in the Genesis' life span, it is all the more impressive.

Thunder Force III
The fire stage is perhaps the most recognizable scene from all of Genesis games
This game.  When I first got my Genesis, I had enough money for the system (which came packed with Altered Beast and a mail-in coupon for Sonic the Hedgehog) and one budget game.  For whatever reason, this game was only around $26 at the time.  The cover art and screen shots looked cool, so I chose it over ESwat and Alex Kidd in the Enchanted Castle.  Boy did I make the right call.  I was so addicted to this game; everything about it was awesome. The weapons, graphics, music, and innovative stages were all so well crafted that to this day it is one of my most played and cherished titles.
The weapons give the player immense satisfaction, as you dole out over the top punishment to the enemies throughout the game.  Couple them with the "claw" (options) and you got some screen-filling mayhem spewing from your ship.
The stage design incorporates the typical tropes of '90's video game design: snow stage, water stage, fire stage, land stage, space stage, etc.  One of the things that sets this game apart is how well each stage is executed.  The wavy fire background was mind-blowing for the time, and still holds up today.  The currents pushing your ship around underwater make you respect the environment.  Hidden power ups can be discovered by taking chances and piloting through dicey terrain and narrow crevices.
I can't think of many other games that pair the music so well with the stage, in fact, I can't think of many other games where I would want to listen to the sound test.  It may be a bit on the easy side, but being a shooter wimp that's fine with me.