It was an awesome game, loved it!
At first I was a bit confused because you can't shoot while you crouch, you can't see where the enemy is looking at easily, was expecting them to notice me when I start shooting and I was unable to kill the guards by shooting their neck (missing the head with a slight margin).
But then it clicked, I found the right angles to get all of them with a single headshot. It still wasn't easy so I enjoyed it quite much. The music and sounds was awesome (kinda wishing there was footsteps as well). Got really scared by that fella in the bathroom :) and was nervous when I hit the electrical switches, expecting more of them to raid (or at least spawn). So it was pretty fun overall, Loved it!
Edit: Also appreciate the mac version.