I don't think Ikaruga was all that hard. It wasn't easy, but supposedly there's a way to win it without firing your guns. You just switch back and forth between black and white and use your special weapon. I can't even imagining doing that.
Battletoads wasn't hard, because I'm certain there was nothing after the fucking speeder bike level. The guys who made it just fucked up and forgot to make it possible to do that level.
The Adventure of Link (Zelda 2) was a hard fucking game. But only really after you start going through those caves to get to the great palace. Up to that point it's easy, but after that it's a bitch. The great palace was a pain in the ass.