Amazing Idea! loved it and would like maybe to see it as a full length game!
a few notes i have:
* I would put a marker on direction of enemies because i had some time i ran through the area without seeing anyone.
* When you shoot the bang you should first time maybe tell the player he must switch the bullet i kept pressing the mouse in panic.
*Love the main menu, but i would in the main menu have different types of bullets. Could give a cool indication on whats to come