Loved loved loved the concept. The kind of game I have in mind when I sit down at the keyboard to write music. Gameplay was really cool too. It's hard, you die a lot, but since there's very little penalty (short levels, fast respawn) it doesn't kill the fun, even for someone who tends to hate difficult games like me.
Didn't love the fact that it crashed on me and I had to shut down the browser to kill the super loud repeating "crash" sound effect looping. Which is the only reason it didn't get 5/5.