Really polished! I like the simple art style and the sounds are pleasant! The concept is also interesting, I think maybe you could incorporate one or two other mechanics to help add more interaction to the gameplay? I like how you have to time the finish on 0, but it often requires a lot of waiting. To stick with the one-button theme, maybe you could add bouncers that only activate when you tap them?
But overall, a well executed concept with a good variety of levels! Really great job!