I really liked the visual style and the overall ambience of the game.
I feel the boss was slightly too hard, I did manage to beat it. I don't think it would need that much tweaks, but I had to exploit the intro where the boss attack less and take half of the HP. I think the main problem is the hands projectile attack frequency, since I have to wait to charge the attack, I have a VERY small window between the hand attacks to charge a shot, so I think that either slightly decreasing the interval of hand projectile attacks or slightly decreasing the player charge up time would do it. Also the "puking" attack was leading to unavoidable hits, for some reason only on the right side of the map and not the left where it would always stop before the wall, would be nice if it would do the same on the right.
Anyway, cool game ! I enjoyed it, was satisfying to finally beat the boss in the end.