This is very entertaining. The gameplay feels super smooth, and your reload animations are awesome. The map is small and gets tiring (as a proof of concept map is bound to be), but the work you've put into the lighting and environment is fantastic. The atmosphere is creepy, and makes me feel small and uncertain. If you make the game a bit harder and add in some zombie and ambience sounds, this could easily become really scary and tense.
I love your shooting, especially considering how early this is. I did really want to hip-fire the submachine guns into groups of zombies and spray them down, but the hip-fire aiming is a bit hit-or-miss. Because of how dark it is, it's hard to see the blood splatter and get a feel of where my bullets are going unless I ADS. I feel like having a basic reticle to show me where the centre of the screen is would help with the hip-fire feel, even if it doesn't adjust for bullet spread. A little dot to help me understand roughly where I'm aiming would be fantastic in a dark map like this.
Overall this is cool as hell and I can't wait to see where you can take it :)