Needed more time invested
The game is, unfortunately, fraught with novice work. The third level had a glitch that prevents you from being able to walk into the cave.
The story really didn't draw me in at all. Basically zombie movies tend to boil down to one of a few things...something from space caused a reaction to reanimate the dead, dark evil magics are reanimating the dead, and (the abundantly overdone and cliche plot line) something went horribly wrong in the lab; now we have reanimated dead terrorizing a small town setting. *Note to self- Do not live in a small town that has some form of research lab that outclasses the revenue of said town by a hundred fold. I would have truly overlooked the plot if it wasn't also for the atrocious grammar.
Graphics were basic. I personally understand how bad you limit yourself when you choose an overhead view, but there could have been more work put into the gameplay graphics. The animation itself is what can be expected of this style of game. A point to remember would be creating more randomized enemies than just shirt color. I would have also liked to see some sort of effect to them for having lost a head.
The enviroment needed more work. The graphics were just overlaid on to single plane. This unfortunately meant there was no height difference at all. On the third level especially you notice this when the bend for the cliff acts as a curtain so you can hide behind it.
Overall though I believe this is a learning experience. With time and work I'm sure you can make a mark with your games. My primary suggestion though is find a story to work with in and then craft that. Afterwards makes the game work to tell your story. For now surge ahead. I hope to see great things from you in the future.