Mm 5 GB is actually one of my favorite megaman classic games. (I count it as a classic series, since it's the original megaman.) I like it a lot probably cuz there's no 'man' bosses. It's a refreshing change. Plus, seeing that Wily didn't make any of them, that increases their appeal. Sunstar was the perfect final boss. Everthing does one damage to him, he has plenty of attacks, and he can burn the floor beneath you. What's not cool about that? Plus, he beat Wily up good. I like that.
The music itself, I think, pushed what limited sound that the gameboy had to the limit. I highly recomend listening to Sunstar's song, when you fight him. Venus's stage is also good, but so is Wily final stage. Also, the stage select screen. Oh, so many good ones.
And, if not for mm5 gb, I wouldn't have been able to make my avatar. It's pretty cheap sprite, I know, but I like it.
Man. I thought ths would've been a short post, but it turned into another rant. Blast me and my capacious lungs.