Copying the powers of the bosses you beat is cool but that means that a boss is either trivial (if you have their respective weakness) or a giant pain in the ass to fight. Furthemore, I would have liked to be able to use the different powers a bit more in the actual stages but that wasn't really feasible since all the powers drain your energy extremely fast and you will want to reserve this energy for the boss fight.
Mega Man controls pretty terribly too. His jumps are pitiful and so is his movement speed. That makes the platforming in this game extremely frustrating and just not enjoyable at all. The only reason why this game was somewhat palatable for me was because I used save-states and even then I found it pretty frustrating.
Also the guy who designed the Yellow Devil boss fight should be shot.