Not bad at all
Could be made a bit bigger, hard to read the text, even on high detail. Cannot make out what it says when you shoot them in the head (Headshot! I'm assuming?).
Clicking to reload is a pain in the ass, especially when you reach about 2:30 or so and it's an endless wave. Just have a reload button set. It really won't make anything that much easier with the endless army you have set up to make the game damn near impossible get to 3m, more or less past that.
Accuracy calculation gets messed up if you shoot multiple zombies in one shot. Really, nothing can be over 100%, no matter how much you try.