The transformations were an interesting concept, the music is nice and the graphics are really great for a Game Boy Color game. But the lack of a map, some design choices (specially in the last labyrinth) and how tedious it is to travel from one place to another kinda ruined the game for me.
It's still okay, and I hope the sequel is better.

It was pretty okay (save for Heat Man's stage), until I got to Dr. Wily's stages...

It's a little better than the first game, but not by much.