Damn, it's hard. But fun! However, +1 bullet for one of the upgrades is pretty rough imo. The gameplay loop is fun and simple, but the enemies like to linger a lot. I mean if I suddenly come face to face with an enemy, it usually means I'll lose 2 instances of health since the speed of the enemies is only a tiny bit slower than the player. The game could also take a bit more polishing such as particles and UI.
Overall, quite enjoyable :)