You need to fix the zombie AI, it's atrocious. The fact that they can glitch through you and hit from the back, the amount of damage they do, and the aggro settings are all off.
Also fix melee; if I hit someone or a zed in the face with a crowbar, that should put them down. Not tank 7 hits with it, and If I switch to fists then it only takes 3 hits. That makes no sense.