Really fun game! This is a true bullet hell.
For me the game length is perfect. I enjoyed the bosses quite a lot! Patterns and music were really good. Hitboxes felt really fair.
I think I've found a "bug" with the diagonal shooting, nothing too serious, but if you hug the bottom of the screen your diagonal shots don't spawn (maybe their hitboxes clash with the walls out of the screen?).
Overall a solid game, I had fun playing it. Bravo!