The player's health doubling as ammunition is a very promising idea.
There were a few issues preventing this game from being as fun as it could be. The aiming was not quite precise--as another reviewer points out, there is an offset. This is a serious problem when it is this important to conserve ammo. Also, enemies spawn in various points without warning. I once had the leech spawn on top of me, and it wouldn't let me go.
I'm not sure if it was my device, but I couldn't get any audio to play.