This is for the SNES version. I haven't played the GBA version and probably never will.
This is my favorite Mega Man game. All the levels are great and the weapons are all really good. I love the music in the levels. I like all the Robot Master fights, the exception being Burner Man due to him going off screen and being really fast, and how the game puts all the easier stages first. The game is hard, but it never feels unfair. Almost every time I died, I was able to see how I died and how I messed up and how I could prevent dying in the future. Both Mega Man and Bass are fun to play as. The game felt harder as Bass, but some sections were harder for Mega Man. The second King stage was annoying since you couldn't save and the bosses take a while, but if I was able to save in between sections, I wouldn't have really cared.
I don't really understand why people don't like this game. If you pay attention, this game isn't really unfair. There's the fire in Burner Man's stage and that one boss that puts you in an acid bath when you kill it and that's really all I can say are unfair moments. I love this game. Also the soundtrack is absolutely amazing.