What a great game! I had really fun playing through the levels and listening to the music. The graphics were gorgeous and I think that you did a good job interpreting the theme as well :)
I saw that a few others mentioned the order of the arrows, and I have to agree on that point. Another thing that I really would have loved would be some indicator of the beat. I felt lost a few times since the space between the arrows are only relative to other arrows and not a constant change in the background color or a vertical bar over the arrow lines.
However, these are minor things. This is still a great game! :D