There really should be a way to start a new round without having to quit and restart the game, especially since this is a game where you die very fast and the gameplay is "hectic". If I could e.g. just press space to start a new round, I'd probably get more into it and enjoy it more.
The visibility mechanic is simple but effective, and makes good use of the theme. A nice thing would have been some audio effects, e.g. a gun sound or if the zombies made some noises that indicate when they are close to you.
The mouse controls are effective, but the ability to move around with the keyboard doesn't do very much for me, in particular since it's hard to judge your position because of the limited visibility.