When we think of HP and what it represents we think of a variety of uses it's seen over the years.
"Hit points, also known as life points, damage points, or just health (among other synonyms), is a finite value used to determine how much damage (usually in terms of physical injury) a character can withstand. When a character is attacked, the total damage dealt is subtracted from their current HP. Once their HP reaches 0, the character will be unable to fight."
In other words, it's a singular value for how much life a character has left in them. I'm of the opinion that having just one value for the character's health has become an outdated maxim. I also agree with most people that having too many HP bars -- such as having an HP bar for every limb and then some -- is a bad idea. Players just can't keep track of that many. However, if you display the right kinds of HP bars in the right way at the right time, the player can keep track of all of them.
What I've done is divided each of the individual qualities of HP into different bars, meters, and scores in such a way that they're easy to manage. They have been named and act in such a way that they match how the human body behaves.
When you're essentially defeated because you can't fight anymore, it doesn't necessarily mean you're dead, it just means you're winded. When your Stamina gets low, your ability to perform diminishes. You become sluggish, you become exhausted faster, and how long you can strain yourself decreases. If your stamina bottoms out, you collapse. (Unless you die from something killing you while you're KO'd, the game jumps forward in time to the point where you regain consciousness) Stamina decreases when you take concussive damage, among other causes such as trying to move around while wearing a suit of armor you don't have the proper strength to use or actions which drain your Ability meter or Concentration bar. Stamina regenerates slower than Ability but how quickly it does so is dependent on your current condition, such as whether you're resting or walking, whether you're wearing heavy armor, how many times you've lost blood, etc.
Most everyone has the roughly the same amount of blood in their body. This means that it doesn't matter if you're built like a football player or a nerd, a bad cut is a bad cut, and if you don't get it treated, you could die. Blood loss is most similar to the HP we know. It decreases when you take concussive damage, (bruising) but it also drains when you take damage that breaks the skin. That is, if an attack breaks the skin, your blood level won't just decrease a set amount, it will drain it continuously until the bleeding stops by clotting or by use of healing items. Typically, healing items only slow or stop the loss of blood, not regain blood. You need rest and/or a doctor for that. (there are blood recovery potions, but they're expensive) Blood loss also drains your maximum stamina along with it, which is why the Blood Bar is behind the Stamina Bar.
When you wake up in the morning, you start to use the energy you built up while sleeping. By the end of the day, you can only stay awake for so long without involuntarily falling asleep. If you sleep late, you wake up late, and even if you slept for more than the recommended hours as a result, you still may not of gotten enough rest to pull an all-nighter the next night. If you are nearing exhaustion, you become sluggish, you can't think straight, and you can't take hits as easily. I believe these effects should be included in gameplay. Assuming you get a good night's sleep, the Exhaustion Timer starts counting down at 12 gameplay hours. (which equates to a day-and-a-half in game time) Anything you do in your waking hours makes that timer accelerate while you're doing it, depending on how much effort you exert and for how long. All those little exertions add up, so typically after a full day you'll end up tired enough to just go back at your apartment and sleep. Additionally, you can tell your character to "wait" if you're waiting for something or "skip" an event or dialogue if you don't want to see it. Both of these advance the game's clock and the Exhaustion Timer. To avoid cluttering the HUD, the Exhaustion Timer only appears when it drops below one hour. (configurable)
This is essentially the stamina meter from Shadow of the Colossus. It's upsetting that we haven't seen many if any instances of a stamina meter like this since Shadow of the Colossus. When this gets low, you become sluggish, and can't deflect blows as easily. It recovers quickly, but can be knocked down by pretty much any kind of impact to the arms or hands, even if it's an indirect impact such as deflecting a blow with your sword. It also drains quicker overall when you attempt to wield weapons you don't have the proper strength to use. Actions which drain your Ability Meter also slowly drain your Stamina Meter.
Hunger and Thirst
Everyone gets hungry or thirsty every once in a while. When you become extremely hungry or thirsty, different effects occur, such as loss of concentration or your ability to exert yourself. Some games have attempted to implement a food system, but most fail by either making all the food essentially the same or by making the different kinds of food so powerful that a character will only eat certain kinds of food because they boost their stats a certain way. That's just not healthy. While it's true that sugary foods can give a sugar rush, that sugar rush is temporary and results in a crash that can't be easily escaped by attempting to pull off another sugar rush. If food's going to be different, it needs to be implemented realistically. It's a statistical fact that gamers don't eat healthy. I'm not saying that games are going to be able to change that but at the very least we should try to not make it worse. Make bread that acts like bread in the short term. Make meat that acts like meat in the short term. Make beer that acts like beer in the short term. To avoid cluttering the HUD, the Hunger and Thirst meters only appear when your character is actually starting to get hungry or thirsty, which is about half-way to two-thirds, depending on your overall health. (configurable)
The last three are not actually in the HUD at all, but might be mistaken for HP.
This is what makes the difference between a tank and a mage. Your Toughness Score is how tough your skin is. The higher it is, the less effective concussive attacks are, as well as attempts to bruise or break the skin. The more of your body that armor covers up, the less your Toughness Score matters, although a low toughness can still cause you to bruise even when wearing heavy armor because of the impact of the armor on your skin.
This an overall measure of how healthy your character is. It's normally at zero, and a non-zero score means you're not living a healthy lifestyle. A positive Body Score means you're overweight, and a negative Body Score means you're underweight. Each condition has its own unique penalties. Exercising (which is effortless if you're going out killing monsters and such) and eating right move your Body Score closer to or help keep it at zero.
Think back to Space Invaders. Those little shields you hid behind weren't very effective protection, were they. Once one took some damage, it was pointless to hide behind it even though there was some of it left. Armor durability shouldn't just be a shield that prevents or softens the damage you take regardless of how damaged the armor is. It should lose its effectiveness gradually as it takes damage. Although each part of your body doesn't have its own HP value, the different parts of your armor do. The more damage your armor takes, the more revealing it becomes, and thus the easier it becomes for attacks to deal concussive damage directly or cut you. Wearing skimpy armor (like stereotypical female armor seen in most games) is just as bad as wearing heavily damaged armor. Both reveal more of your skin to the attacker.
HP has come a long way since the days of Space Invaders. It's time we started treating skin like skin, armor like armor, and stamina like stamina.