I feel the second boss was way easier than the first and that the third boss was a big jump in difficulty. I think lowering the difficulty in some indirect way would have been good, especially for a game jam game. Maybe slightly increasing the player's fire rate or decreasing the boss's health, that way its still fast paced but doesn't take as many attempts to win. Or maybe just making the first boss easier, that way most players will complete the first two boss's and get to at least see the third before probably giving up.
I did eventually kill the skull boss with a time of 498s. The SFX for getting hurt weren't obvious enough I feel and I would die thinking I had an extra heart when I didn't.
The artwork is cute and each boss felt unique enough from each other. The game was fun enough for me to struggle through the final boss but I'm not sure everyone will. The SFX fit the aestheticsnicely. The music was good too; on the first boss though, the track sounded like it went off-beat at one point.
Overall a really cool entry. Fits the bullet hell theme very nicely and was genuinely fun to play.