>>12161842 (OP)
Gradius 1 and 2 are fun and fair but I think Gradius 3 ironically takes the series to the next level by being fucking batshit insane and unfair
Gradius 3 is a game you can play for 100+ hours and still not be good enough to 1cc it
For better or worse it has insane longevity. Also, the type select and weapon edit are cool.
Overall I think the best in the series might be Parodius Da!, it takes Gradius 3 but makes it a little more palatable to players who don't necessarily want their cock and balls tortured. Gokujou feels a little too samey. Sexy Parodius is an excellent game in its own right but is also insane in different ways than Gradius 3.