Really great idea for a rhythm game. Only feedback I have is that I'd really like it during gameplay to know if I'm a bit late or early so I can adjust my play. Also some different songs on each level with different beats would help mix things up.
Also finding some way to highlight the difficulty options would be nice because I suck at rhythm games, and totally needed the easier setting but missed it my first time through.
Love the music though, and the minimalist art is quite charming. Great work!