I have an idea for a health mechanic I don't think anyone has used

Instead of just a number which represents how much health you have, keep track of pints of blood. Wounds cause you to bleed faster ("health meter" drains more, essentially), blood loss causes weakness and when it gets to a critical level you die.

So lets say your character gets a nasty cut on his leg and loses half his blood. You can bandage it up and he won't lose any more, but he's going to be weakened until he gets a transfusion.