10 - Darius Twin
9 - Biometal
8 - R-Type III: The Third Lightning
7 - U.N. Squadron
6 - Parodius (series)
Everything about these games are wacky: the selectable characters, enemy designs, the weapons, the stage designs, the music and sound effects, and the bosses. There are a variety of ships/animals/beings to choose from, each with a personalized set of weaponry.
The only thing from completely making light of the Gradius series is the resident difficulty. One would think that such a light hearted theme would allow for some ease of gameplay, but make no mistake, these games are Gradius games at heart. Still lots of fun, though you may want to slide the difficulty down if you want to see all of the stages.
5 - Aerofighters / Sonic Wings
4 - Axelay
3 - Gradius III
2 - Macross: Scrambled Valkyrie
1 - Space Megaforce