This game controlled very nicely and felt super satisfying to avoid obstacles.
The boss design was good, but the arena design seemed strange to me. To maximize my chance of finding attacks and healing I had to position myself somewhere that I couldn't really see the boss. A large number of the attacks didn't seem to really originate from the boss, and when they did, the attack incentivized me being far enough out from the boss that I could no longer see it.
I really enjoyed the music, but the mixing made it sound a bit muddy.
The art was perfect for what you created. Just enough detail to be interesting but still maintain the simplistic design.
I know some of the stuff I said was critical, but I really did enjoy this one quite a bit. You did an excellent job!