I remember when I 1cc Gradius the first time. It took me about a week of serious play on it... on my best run I managed to get at 2-5 , but I never beat the 2nd loop of it. I still think the original Gradius is an awesome game.
The series IMO goes like that:
V > Gaiden > II > I - III - IV
Gaiden is really utterly awesome, and it's the pinnacle of the Gradius gameplay. Everyone should play it someday.
And about V, it's pretty much what Herr Schatten said, V plays nothing like the other Gradius games, so you may or may not like it. I think it's one of the very few games where he and me disagrees about
