Three examples of games I felt did the health system really well; any of the Stalker games and Farcry 2 (even though that game was pretty mediocre in my books) and Battlefield Bad Company (singleplayer specifically).
Stalker;
You get shot, lose health, possibly start bleeding.
You get hit by a mutant or flying object (other than bullets), lose health, possibly start bleeding.
You walk into an anomaly, fall from a height or anything else potentially damaging... you lose health.
Unless you are carrying an artefact which regenerates health for you or are wearing armour that has some form of life support which does the same, you do not regenerate health. Added to that you can start bleeding after being hit, which, if left untreated will kill you; some mutants and weapons can cause such bad injuries that you bleed rapidly, meaning unless you apply bandages, you will die in a few seconds. Artefacts and armour that regenerate health rarely come without strings attached; most artefacts pump out pretty bad radiation and the armour usually has penalties; i.e you can't get another kind of modification for the armour.
Farcry 2; your health bar is divided into segments; within a segment, your health will regenerate to the top of the segment, but no further, forcing you to use a syrette (the game's equivalent of a health pack), which you aren't allowed to carry that many of. If your health goes into the final segement, you start bleeding out unless you get into cover and rather graphically fix the issue; I was playing multiplayer and when I did that, the character started pulling out broken teeth and I was like "bleeeeeeeeuuuuuuuugh! In fact, pretty much all the animations are nasty, but that was the one that freaked me out the most.
Battlefield Bad Company;
The Good
You carry a hypodermic needle called the auto-injector
It has infinite uses
The Bad
It has a cool-down between uses
The very bad
You will get shot a lot (unless you're paranoidly careful)
Only the assault class gets it in multiplayer (and you have to unlock it first)
Your health doesn't regenerate at all, so in singleplayer you have to use the auto-injector and in multiplayer, you have to be assault and use it, be support and use a health crate or go to a support class and get him to heal you.
All three of these work and force you to conserve the use of healing items, especially considering how easy you can die in all three on moderate or higher difficulty.
Can't deny though that CoD's 'jam on your face' system doesn't work though... of all the health regeneration systems, its probably the best IMO. I always felt that RSV2 didn't need one, considering you practically died instantly anyway.