I can remember renting Mega Man as a kid, and getting frustrated because I couldn't beat it. That Christmas, my grandmother had bought me Mega Man 2 and at first I was pissed because if I couldn't beat the first one, the second would be impossible! (Just so ya know, in the first one, I had trouble with the platforms in the Gutsman stage, then later with the first Wily boss) Well, I managed to beat 2, and I went back and finished the first one, and I've been hooked ever since.
Megaman 3 was the best, but had some weird box art going on. I STILL think he's shooting Spark Man in the nuts.