Quite interesting idea. It's a clever way to use and teach scales.
Maybe the game could be more clear on which notes can be played, and which can't. It took me a while to figure out what I was supposed to do. It could show more explicitely whoch keys should be avoided, and when the player jump on a wrong one, use a little animation or color.
It's nice to see a game using a system based on music theory, and playing dynamic music on top of that!