One of my favorite (albeit annoying as a player) health regen systems was in Riddick. You get X squares of health (where X starts at 4 and grows as you go through the game) each of which can be regenerated up to its maximum if you stay hidden for a few seconds. For instance, you take a shot across the abdomen, you lose 2 & 1/2 of your 5 squares. Hiding regenerates you only that 1/2 square you lost. You need to find the health cartridges in order to use the health machines in the athena (or butcher bay).