Interesting concept, I don't think I've seen a shooter music game quite like this before. It may have some potential if you polish some things and make the gameplay mean something. The music is great!
Improvements: Add something to keep track of hit accuracy, boxes missed and show it on the UI. If you turn around, the character gains a lot of velocity and turning back to original direction after a moment going the other way breaks the syncing of the boxes. I spent a good minute of silently shooting at boxes since I went back quite a bit. On the second map there is no detection when you fly off the map. I turned around, flew off the map and kept on gaining velocity till it broke the game.
Keep at it!