Wow, really great game! A fun concept and the plethora of abilities kept things interesting.
The gameplay was super challenging (I never managed to get through the 3rd boss phase), but was quite a fun bullet hell. I think telegraphing the bullet positions a bit more might (maybe just by making the arena a bit bigger), could have made it easier to figure out what was going to happen next. I was mostly relying on memorization on my later runs. Then again, my reflexes suck, so I totally respect keeping the difficulty curve.
I absolutely love interactive soundtracks, so the fact that the music was tied to the attacks really made it for me. I also liked the chiptune rendition of The Bidding by Tally Hall for the menu music :)