Nice work -- this was a fun game and I enjoyed the aesthetics. The low poly fires and flickering lighting were really nice, and together with the excellent police car sounds made for a great atmosphere. I also really liked the animations (picking things up, limping, crouching). I liked the emphasis on stealth, too, which gave the game (and use of the map) more of a puzzle feel, and added to the feeling of suspense. The map itself was also well designed and reliable, and the game thumbnail is nicely designed.
In further development, I would make sure the gun reliably registers hits in close combat -- at times I unloaded a full gun point-blank on the alien, and most of the shots seemed not to land (no red animation). A second suggestion might be to allow the player so slide along vertical surfaces a bit more easily. When I moved along a curb, e.g., it would stick and I had to back up or side-step to proceed. A minor thing, but it might improve the flow of gameplay.
I made it through to Chapter 3 and had fun playing it -- nice job!