Good concept overall, but I had a few issues with it.
The bullet hell aspects worked well. The rocks were pretty hard to hit, and when it got to the third phase all that appeared on screen were the bullets and kept dodging for a few minutes. Menu said to click the boss, but as far as I could see there was nothing to click (perhaps this was a bug).
Still, good job on getting a bullet hell with good patterns in, and multiple phases. Not all game jam games can get this aspect right.