This game is not bad. It has some potential but needs to be expanded. I like TPP view and the flashlight effect that follows your aim, it adds a bit of unsafe feeling, you actually need to look around so z's won't come too close. And I like how you see zombies far away in the fog (though at some point they disappear and spawn close to you out of nowhere).
What needs improving is:
1. Difficulty. It's very easy to get all 3rd rank weapons and then there is no problem in winning every level. Maybe rise prices? Also, barrier is quite useless, it's not very often when zombies come close enough to hit it. I would say that rise the price and lower shield value.
2. Gfx. It doesn't look bad but animation could be a bit smoother (especially blond female zombie, when she get's hit she bends in half, it doesnt look good and makes it harder to headshot). Also, zombie games should be violent, maybe shot-marks on bodies where you hit them? Would add a bit of spice I think. Also, the menus could be bit more polished.
3. Completing the level. It kind of refers to 1st point. Honestly, when I finally feel like I'm going to be eaten and zombies are all around my barrier - the night ends... My solution: change mechanics so that it will be necessary to kill all spawned zombies to finish level.