In the web version the mouse frequently bugs out, but that is probably beyond your control. It's pretty solid otherwise, a few things I noticed are mostly audio problems. The gun could use a much more heavier sound, it feels pretty weak, and the enemies making some noise would be useful, as right now it's impossible to tell if there is something behind you.

Gameplay's pretty good, it plays like the good FPS games. Those box enemies are creepy as fuck, I hope you implement more enemies and features.