Mega Man III

[A Black Falcon]

Actually, while with many games and series the NES versions were better than the Game Boy ones, with Mega Man the GB titles are just about as good as the NES games. Mega Man IV and V on the Game Boy are particularly great, but III is amazing as well... they are very, very impressive games, as or more difficult than the NES games (II excepted, that one is disappointing and easy, and has the worst music quality of the series too).

In MMIII, Dust Man's level is the hardest of the eight bosses, and it's almost certainly one of the hardest levels in the entire GB series... perhaps beyond too, I'm not sure.

Here's a video of the level. This guy's pretty good at Mega Man games, but even he says he died twenty times before he beat this level. http://www.youtube.com/watch?v=PLy6ZYhpMpE