I really enjoyed the concept and the visuals! The music is pretty great, and it makes all the rhythmic aspect of the game really fantastic!
It's very hard though. Some patterns seems unavoidable, but that's still okay. My biggest grief was the aiming. I just couldn't hit that boss, and eventually just shot randomly! (spoiler: it wasn't a winning strategy either)
The game is still fun, and provide a great musical experience. Congrats!