The opening cutscene was cool, I wish the rest of the game kept that style. for the first level, the enemies are total bullet sponges, i'd recommend revisiting the balancing there. other than that I think a stationary but non-rail shooter is an interesting idea

Graphics on the beginning movie looks great. The zombies look spooky and detailed. Starting on level one the zombies just come out too quickly. You should lower the number of zombies and give the player a chance to ease into the gameplay.

Also, you should give cash for each zombie you kill. That way the player could quit the level and go back to buy upgrades.