I hope to see the final product
This is quite good. The graphic style, although rather unnoriginal, is still good. Some things you need to look at in the full game:
-The gun when faced to the left of the character is upside down, shows laziness in coding, consider revising.
When a Zombie is shot it plays the shot sequence there are two faults in this sequence:
1. The Zombie turns to face left even if it was facing in the other direction to start with.
2. You can not shoot a zombie when it is in the 'being shot' sequence, this doesnt have to be changed but consider doing so to avoid annoying you audience.
Apart from that quite a good little engine and it makes the real game look promising. There are errors in the Zombies after awhile but you did state that so I imagine you are working on that now.
Good Job.