I really liked this game! I was a huge fan of Crypt of the Necrodancer (and am a musician) so anything that incorporates rhythm into the game is always a lot of fun. I wasn't able to beat the boss, but since I sucked at another rhythm game that incorporated the mouse I'll just chalk it up to being left handed and that hand being more used to having to be "on time" when playing guitar/bass.
Great work! Wonderful art, great ideas, and kudos for making a song/sfx that doesn't really ever appear to get grating no matter how often I heard it (I died a lot). Writing looping music like that is tough.