This game was done mostly well. I like the concept of an old school arcade "shoot the screen" kind of game, but it was heavily impeded by not being able to see where my mouse cursor was. I also felt like I was fighting rotating the camera while trying to place my (invisible) mouse cursor on an enemy. I think being able to reload before you empty your clip would also help.
Having enemies come at you from the front and back is a great idea, but I think some indication to turn around would greatly improve the experience. Overall, this was pretty well done.