Very visually impressive game. Shooting was rather satisfying as well.
Level is lit well, the terrain/map models are clean and simple. Enemy model looks quite creepy too. I have played a few FPS Jam games before, and this is by far the best looking one I've played. Especially impressive you've got it running so well and looking so good in the Browser.
The music adds to the overall atmosphere, and the SFX you have are high quality and fit in well.
For improvements, I'd recommend adding an aim down sight, or add a crosshair. It could be awkward to aim at enemies further away.
As some other comments have mentioned, some feedback for when you take damage would be good. I felt that there was a couple of places where a SFX would be helpful to give some feedback to the player.
Overall, a strong submission. Well done!