Great, addictive
Great idea for a game. A few things I would spice up: make the music loop indefinitely, or choose a different song that does -- in the later levels you wind up playing in silence which is strange when you've had that bouncy melody going through the whole game before that point. Also, consider having the characters jump around or walking or something to add a new dimension of challenge to the game, even in the easy levels. This might quiet some of the critics who find the game repetitive and would enhance replay value.
The sound effects are cool, the characters are funny looking and the music is pretty neat. A fun little game.