That was really damn cool! The art and atmosphere is very eerie. Enemy encounters and and bosses were quite balanced and fair.
A note about the audio: Whenever there's a very large number of sphere explosions, a bit too many sounds stack on top of each other, to the point where it peaks at +0.5 dB. Maybe at a certain concentration of explosions, it could be replaced with a singular, boomier sound?
Great work!