I was thinking about how much I hate hit points. When I was playing D&D as a kid and earning levels it was the first thing I latched onto as a symbol of power. Lots of hit points meant you could survive fights longer so in kid logic it meant you were tougher. When I started looking at how the classes had different rates of earning hit points I started to question the rules, my first finagling doubts that D&D wasn't perfect. About the same time I started reading Dragon magazine and if the pages of Out On A Limb (and later called Forum) are to be believed it was a subject of much contention that hit points made no logical sense. That some PCs could achieve triple digit amounts of hit points only added fuel to the fire. It's also a bit of a joke, a 1st-level wizard can be taken out by a housecat due to his abysmally low starting HP.
The game HOL, Human Occupied Landfill, had a rule that every living thing has 20 "hit points" and damage had different thresholds which were adjusted by size and damage type. Hit a bunny with a hammer and you'll cripple it if you don't kill it outright. Hit a man with a hammer and you'll do some damage. Hit a man in powered armor with a hammer and he'll laugh at you. In theory it made a lot of sense but in practice it tended to be wonky and weird and too much math, thus no fun. But the idea really appealed to me and has stuck with me ever since I first read it.
There's a need players have to gain in strength and power as they advance their characters, and there's also a need for some level of realism that allows a suspension of disbelief. It occurred to me the other day that it would be very easy to fulfill the two by returning to the idea that everybody starts with the same amount of hit points but relative to who they are they can increase, without the need to alter anything in the rulebooks.
Every PC has 5 hit points and adds their current level. Constitution modifiers now count as double, but are only applied once.
Let's look at it in practice:
1st level Wizard with CON 10 = 6 HP
1st level Fighter with CON 10 = 6 HP
1st level Wizard with CON 15 (+1) = 8 HP
1st level Fighter with CON 5 (-1) = 4 HP
Now there's a real incentive to NOT have a low Constitution starting out. But this equation does create one obvious problem: How do you compensate for monsters' hit points? All those stats with varying levels of Hit Dice? Another simple equation that can be done just by looking at HD under a monster's stat block. Monsters get 1d8 for HD, so their equation is MAXd8+level. But this creates another question: what about when a monster has a +1 or +2 next their HD number? Just add it to the total. A monster with HD 3+2 would then be 8+3+2 = 13 hit points.
How would this look?
Ogres have HD 4+1 = 13 HP
Trolls have HD 6+6 = 20 HP
Young Red Dragons have HD 13 = 21 HP
Adult Red Dragons have HD 17 = 25 HP
Armor Class becomes a much bigger factor at higher levels now. Ogres have AC 5, Trolls have AC 4, and those Dragons have AC -2 (Young) and -4 (Adult). This greatly enhances the perceptual value of seemingly "low powered" magic items as well. Having a +1 sword suddenly becomes really valuable to the PC wielding it. I haven't looked at books or tables beyond 1st or 2nd edition AD&D so I'm not sure how it work with 3rd edition books, I know some monsters are given different die type so I would have to account for that, and I think magical damage probably needs to be adjusted to compensate for the low numbers but for now I think this works pretty solidly as a simple and elegant system to build off of. Leaving it as is means that Wizards become MUCH more powerful earlier on (casting Magic Missile at 3rd level is possibly deadlyand 5th level Wizards basically become murder machines), and 5th level or higher Clerics can basically heal anybody instantly (maybe kind DMs would allow healing to "bleed" off onto multiple targets).
* - in 1st edition AD&D some monsters were given HUGE modifiers to their hit points, probably to ensure they were difficult to kill regardless of what the DM rolled