This game is fantastic!
Just got it from the Equality Bundle.
There are only really two complaints I have, and they're both minor (there would be three, but the creator has already said the mobile version will add more content).
1) Ammo and health almost never increase substantially. Maybe lower the starting health but make max hp upgrades more plentiful?
2) Each time it loads something while in windowed mode, it forces itself back into the center of the screen at full window size. "Full window size" meaning that 80% of it is just red to the left and right, constantly forcing itself into a size that it doesn't even use most of.
Oh, and just beat the final boss.
Creepy, fantastic.