Literally 2 frames per second on my macbook. Based on my own experiments with Unity, I am sure it's fillrate-limited. Optimization would involve using simpler shaders, a smaller screen size, or both.
Mouse movement feels extremely limited if I use my actual mouse. Using a laptop's mousepad felt more natural-- a single swipe resulted in about 8x the speed of using my mouse to perform a similar swipe. I recommend adding a mouse sensitivity slider that can go down to 10% and up to 1000% to accommodate different users on different setups. This should be on a menu available with one click from the pause screen as well as the title screen.
Once I managed to pick up some shotgun shells, I walked forward into the left-hand door and turned left. It was dark so I instinctively pressed F to try and turn on my Flashlight. Nothing happened but I started taking damage. I based into the shotgun room and saw that there were two black monsters on a black background killing me. Pressed fire several times but the shotgun only fired once. Not sure which kind of lag was responsible for this death.
Overall, the game felt unplayable on my computer. If you won't optimize the graphics, how about some recommended system stats?
Note: I can play FPSes, including Unity FPSes, on this computer. I just can't play this one.