Good job for a first game :D
Giving player the option for turning off music would be great. Id like to hear only the sound of the pistol firing and zombies - just out of curiosity. Music sits well with the theme thou.
I also missed some sort of animation of zombies dying - falling on the floor or something.
It's actually pretty good. I scored 3600 points. Am i pro? XD
The music is good, and the graphics ar not bad either. I'm glad it had all the necessary menus.
Next thing you could improve on is making your game more juicy. It could use some better animations an effects, specially on zombie death and player death. They are too sudden.
Shooting and reloading animations could be better as well.
Shooting could feel more powerful if the pistol had a stronger recoil and muzzleflash. Look at how far back the gun kicks in this animation: https://www.youtube.com/watch?v=J1kYjYAO8r8
The camera even shakes with it.
Reloading could be more dynamic as well. Look at this one for example: https://www.youtube.com/watch?v=6LYgK55v1Rk
It's probably not so easy to make, but it would make the game look much more polished.