This is a very well designed and executed game! It feels like a feature complete mini game with the correct amount of polish, great art, and charming music, and great game feel. The mechanics are simple and it really lets you get in the flow state. You've got a really great difficulty curve with each level adding new mechanics, I was pleasantly surprised when you could start choosing the track you proceed on.
I think the only real feedback I have is that you should be able to restart the level with the space bar after you fail.
Incredible job!