It has potencial, I recomend:
1.- Upgrade the ADS, games with iron sigths are good
2.- A bolt action rifle (like a Mosin-nagant, M1903A1 Springfield or Mauser Gewehr 1898) and a Lever action shotgun

The AK47 and the M4A4 both have a glitch that occurs if the left mouse button is held down during the reloading animation, resulting in a substantially increased rate of fire, as long as the mouse button is being held. if you release and press again then the rate of fire resumes to its normal rate, although it is more fun this way tbh.

It needs some work, but its a good start.

I think you should add a shop when you first start the game or after you die, so you could buy better guns after gaining money from killing zombies. Adding a shop would make the game more fun because you have better weapons during zombie combat, also. I think you should add more zombie types, like running zombies or anything else that comes to mind. That would shake some things up if anyone playing got tired of the same old slow zombies. I think you have done a good job so far, you just need to polish some things up.