Beat with 3 hearts to spare. The different phases pace the game well. Pleasing color scheme. I love the whole "idea" theme with everything, it's cohesive. Music is great, except there's one part where the melody sounds drunk lol.
Ok so the difficulty curve is weird, it seems that when you have 1 wide bullet the game is the hardest, harder when the brain falls asleep, but then kind of gets easier for the rest due to having wider shots, at least that's what I've found.
The mouse controls seem to get really bad when testing on slow hardware, unplayable as if it records your inputs and plays them back whenever you move the mouse, and it gets worse and worse. Playing in a small window becomes weird as the player can get desynched from the windows cursor even at 1x sensitivity. I had to play using WASD.
Game felt a little short, and the boss got a little same-y until it split into 2 halves that part was pretty cool. But still, no projectiles are added after the Z's so it can get a little stale even for the shortness of the whole game.
Just a few gripes, on the whole I loved it. Great work.