This game's awesome! I think the difficulty curve was actually pretty great, although I'll admit level 7 was too tough for me (I think I figured out what needs to be done, but I didn't have the patience to keep trying).
Love the music! My only critique there is I wish you didn't change tracks between the levels and level select, because it meant the music would keep starting over and I'd never get to hear the really sweet parts. Alternatively, being able to restart a level (without restarting the music) would work too.
Really liked it overall though!