It's allright but nothing really sets it apart from any other platformer.
Graphics are pretty good. Prety detailed, the areas look nice. The music was good, it used some familar Disney music that you'd probably come to expect considering this is a Disney game. The best part, in the graphics and sound is the Disney stuff even if you don't like the movies. The level design adds a little excitement. It uses different movie themes from Mickey's past and without it, this would be as dull as a rock.
Gameplay is average platforming. You'll visit places all over Mickey's universe, like Steam Boat Willie is the first few levels. Platforming is mediocre at most. Nothing really sets it apart from any other platforming game. But then, like 50% of the NES and SNES games out there are platformers so...
If you're a little kid, a Disney fan or if you must play every platformer than go ahead and try out Mickey Mania, but I warn you, you're not going to see any new gameplay twists and changes. Just same old, Disney style.