Hey, this game has a direction it's going for but it's a bit weird in my head currently. I'll explain more later, first a few things I quite like:
Very good sound design here, worth commending. It gives very good feedback, and an audible indicator for when you are low on health really helps. I think you did a tremendous job here, one way better than I expected!
The art is simple, but very well done! I'm sure if you had more time on this, it'd look even better!
The music can get a bit obnoxious after a while and I had to lower the volume of the game before getting sick of it even in the few minutes I played.
I think my biggest gripe was the whole game design, shooting itself deals damage to you - which is very contradicting and off-putting if not done right. I think your biggest missing link now is to enable the player to shoot more people per shot. I think if you added a way to kill multiple people at once, it might spice things up, such as charging your shot to penetrate enemies or if you richochet your bullet off a wall, it will gain the ability to penetrate enemies, etc.
Also the aiming is a bit weird.
Anyway, nice!