Very cool concept and great execution! I like the fact that you're essentially shooting enemies with your own HP bar, and that it is made very obvious through the visuals.
Small improvement ideas:
The healing animation scared me every time since it looks as if I'm taking critical damage.
The amount of HP we have to shoot out seems too high. It would have been nice to make picking up the blood stains more of a challenge, since now it doesn't really matter if you pick them up on almost full health or not.
The enemies are as smart as cucumbers. For me most of the gameplay was waiting for them to get stuck in the hallway.
Still, great job in this limited time frame!