Ninja Gaiden II has a pretty balanced difficulty. 1, on the other hand, is really brutal at the end with some near impossible platforming, complete with the oh so lovely "bird knocks you into bottomless pit" combined with "losing at the boss kicks you back 3 stages."
I've been playing Ninja Gaiden 3 (japanese difficulty) and it's been kicking my ass as well, but I am totally unfamiliar with it. It's much harder than 2 but (so far) easier than 1.
My vote goes to that level of Castlevania where Death is the boss. There's a trick to it, if I can get and keep the holy water (the game gives you one at the start of the level) then I can get past the last part pretty easily. Holy water makes the Medusa heads, the axe knights, and even Death pretty easy. But if I don't make it to the end with the water...holy balls, it's either play perfectly or die horribly.