This is a seriously cool game, especially the sound!
The jumping pitches (that follow the harmony and change depending on if it's the first, second or third jump) is really inspiring, as is your solution with different parts that follow how well your doing.
I kinda like the laid back drum beat, it's a cool contrast to the fast pace of the game. Perhaps you could either increase the tempo slightly faster the game goes. Or make the drum track play sliiightly more "on beat" the further along the player gets.
The mechanics are very simple, innovative and work really well. Like MurphysDad said, I don't really see when I should choose which character. So perhaps something could be done to the game design to make the characters shine in different parts.
The graphics are solid and look really professional. The one thing I had wanted at least when I started playing was some sort of running animation for the characters.