I've always been an action gamer at heart, starting with the original Duke Nukem sidescroller from 1991. A main part of my upbringing in games has been first-person shooters, and shooters in general. From time immemorial (and for gamers, the 1980s are time immemorial), the standard currency to represent a character's resilience has been hit points (HP), or sometimes just health.
The most commonly referenced origin story for the concept of HP is the original edition of Dungeons & Dragons. The original D&D was derived from a wargame called Chainmail -- specifically, a scenario in which the advancing army must penetrate a castle's dungeon to come up into the main courtyard. Players enjoyed the dungeon scenario so much that Gary Gygax decided to make it a game in its own right. Of course, with a party of four or so characters, dying when you failed a single combat roll sucked, so he invented hit points, a measure by which a character could take some amount of damage and continue fighting.
Action games usually subscribed to one of two philosophies for a player's resistance to damage -- either he died in one hit (and usually several lives), or had a stock of hit points, called by various names, against which damage would be applied. Hit points could usually be restored by various measures, allowing a player to progess through much or even all of a game without dying given sufficient skill.
Arguments have been made, however, against the realism of this flat "life bar" system -- it fails to take into account the physical effects of damage to a human, for example. This degree of realism scarcely mattered in the games of yesteryear, where attention to detail was the exception rather than the rule, but since games are becoming more and more detailed, more and more realistic, and since player expectations have grown, some attempt has been made to address the percieved shortcomings of the hit point system.
One rather persistent trend seems to have taken root after the release of Halo, and particularly Halo 2. Halo used a system (which had appeared in games prior to it) wherein the player's HP was divided into a "shield" and "health" gauge. Shields would absorb the brunt of damage until they reached zero, and further damage would be applied to the player's health. Shields regenerate after a couple of seconds if the player doesn't suffer further hits, but health does not. Halo 2 removed the health gauge entirely -- the player still has a stock of health points, but they are not displayed on screen, and regenerate over time (at a comparatively slow rate).
I have always particularly liked the shield/health system from Halo 1 -- to tell the truth, I liked Halo 1 better than the other games in the series as a whole, but that's another discussion. The recharging health system has a handful of effects for gameplay:
- Increased short-term lethality. Almost universally, the recharging health system brings with it a reduced HP maximum -- the player will die in a few shots if he does not seek cover to let himself recover.
- Simplification of the supply dynamic. Games with recharging health need not provide the player with items to restore his HP -- it happens automatically over time. (The console version of Call of Juarez is an exception -- while the PC version had a strict HP counter, the console versions allowed the player's health to recharge, but left in the liquor bottles as a way to immediately recover HP.) Not having to include health packs means that the game no longer has to analyze that variable in the long term, meaning it becomes easier to balance encounters; the player is never in a low-HP state to begin with. The downside is that game effects that use HP as a cost variable (collecting items through hazardous terrain, "rocket jumping", special effects charging the player health points to use) are no longer a valid design decision, as there is no real consequence to the player unless he hoses up and kills himself.
- Simultaneous increase and decrease of realism. This one requires more explanation.
Recharging health systems have an odd effect on realism -- it all depends on the player's frame of mind. Combats become more realistic for two main reasons: First, the much decreased maximum HP count. Real people tend to die (or at least become incapacitated, which in most action games is as good as death) after just a hit or two. Since the player cannot have a large buffer of health to fall back on, it "knocks him down a peg"; he's no longer a Superman, but an average joe in a rough situation. Second, gunshots and other attacks often inflict much in the way of physical and psychological trauma, but may not have much lasting effect in the case of "flesh wounds" or wounds that are properly treated. I suppose some hand-waving is assumed in which the player character seeks medical treatment or patches himself up between scenes.
It is that "hand wave" that provides the decrease in realism as well: the player is essentially invulnerable, as long as the bullets he recieves are evenly spaced. A character could suffer a hundred or more hits against a life bar that lasts as long as three or four, and still survive with no long-term ill effects. I don't intend to argue for the inclusion of long-term damage effects in a game like this, as the player as a matter of course suffers far more damage than any reasonable person could be expected to absorb, and he must for the sake of the story keep going. Inflicting some kind of permanent penalty means the game would become a drag very quickly for anyone but an expert player.
This dichotomy becomes perfectly clear in a few recent games. The most standout example I can think of is the Rainbow Six: Vegas series. Tom Clancy's Rainbow Six series of games has always been notable for very easy player lethality. The original squad-based combat games would find characters out of action or even permanently killed if they suffered more than a hit or two; the effect is mitigated by the fact that the player had a roster of twenty or more characters, and an endless "reserve" stock of soldiers. More recent games, such as Lockdown, were more action-oriented, but still had the player suffer much damage from enemy shots -- the player's lifebar was quite small, and characters could not heal in the middle of a mission, in a nod to realism. In the Vegas series, the player's very low HP total returns, but Ubisoft has opted to include a recharging HP system. It's realism without being unfair, on a surface level. But for a RS game, it seems odd to include characters that can suffer dozens of hits, and in fact are largely immortal given enough adrenaline shots in the buttocks to keep them going. (The player is the sole exception -- if his HP reach zero he's down for good.) It makes for a better game, to be sure, but it does require some serious suspension of disbelief, particularly among series congnoscienti.
To tell the truth, I don't understand what's wrong with the good old lifebar. Even Tom Clancy's Ghost Recon included a fixed health system (and a medic character to keep the player and other characters going). I can see how the recharging health device is useful for some games, but it tends to crop up in places it doesn't belong -- RS: Vegas, but also such games as Uncharted: Drake's Fortune, where the protagonist is intended to be an everyman stuck in an unusual situation. (This is a textbook example of a phenomenon called ludonarrative dissonance -- a mental block occurring because the demands of the plot clash with the demands of the game system and mechanics. That's still another discussion.) It's a tool for simplification, and a handwave against realism. If you want realism and limited HP, give the player a realistic way to heal his wounds -- bandages, a medic, something along those lines, rather than a glut of medkits stored in unbelievable places, and leave the magic healing devices for sci-fi or fantasy games. Or strike a compromise.
An interesting system I saw came from a slightly older PS2 title, kill.switch. The player had a dual-layer lifebar, which for the sake of brevity I'll refer to as "stamina" and "health". When the player suffered damage, a significant amount of the trauma was applied to his "stamina" bar, which overlaid his health. The health bar suffered a small portion of the damage -- something like 20-30%. If the player's stamina bar ever reached zero, he died, but given time to recover, it would fill to a maximum level equal to the player's remaining health. He was able to suffer only a few hits in the short term, but there were still long-term consequences for suffering damage: a reduced capacity to absorb further hits in later battles. It left the player to make tactical decisions about how to approach battles, and didn't depend on him being in perfect condition; also, it satisfies the realism demands of a low HP max as well as accruing wounds over time. It's a system I wish I saw used in more games, and one I intend to test out if I get around to making a pure shooter game. More on that concept later.