I think that you should add wasd also for moving
But the main thing is that you need to make the character move/rotate about its axis like move the gun 360 so that it would be much easier to control the character !
so that you could move it a different direction and still be able to shoot at zombies
So that you don't move but can point and shoot in any direction
Since there are way too many coming at you.
Also there are regular zombie freezes where they all freeze for a second or to then start moving.
\Don't know it that's a glitch or you made it so that the player could have some time to move away.
And some upgrades to the gun would be nice.
Cus i don't know if you played it yourself to see just how many zombies come at you.
Anywap good job and Good luck further !