very good
overall very nice, very fun.
However, I made this review to contribute an idea: How about you make the melody harmonic, and have chord changes every so often? So you have some kind of song. It could be like, every level is a song, maybe like C, F, G, F, C, G, C. And as the levels progress, the harmony gets more complex, adding 7ths, ninths, and stranger modulations. Well I hope i did not confuse you with music jargon, but if you understand what I'm saying, I think you should give it some thought