As a D&D5e DM, I always feel that HP in D&D are somehow unrealistic. Either it's "there is no difference between 1 HP and 100% of my HP" or "I took too much damage in one hit, so I'm dead".
So I tried to make a houserule somehow inspired by the Vampire: the Masquerade HP system.
Here's what I ended up with:
Each time your character takes damages that reduce them below 50% or less of it's current HP (on one hit), it takes a penalty, which becomes stronger each time it occur (reset on long rest)
e.g. you have 100 current HP. You take 50 (or more) HP of damage on one hit. Your character get a penalty. Now it current HP are 50. So, if it is not healed, it will get another one if it takes 25 (or more) HP of damage.
First time you have disadvantage on your rolls until your HP are restored to 100% (or you are taking a long rest).
Second time something broke in you (your arm, your leg, etc.), which will give you disadvantage on rolls using this limb.
Third time you take a permanent wound (a.k.a. you have this disadvantage until you got a regeneration spell or equivalent).
Fourth time you are dead.
Is this houserule balanced? If not, what could I do to improve it?
Balanced compared to what?"
I mean balanced compared to the actual system, or compared to the alternatives (DMG, Unearthed Arcana)
Implementation issues already considered:
How difficult is it for me to keep track of enemies and their HP reductions? Since I use Roll20 as a support, it is not that hard. (so I can guess that most of combat tracking app could do the job)
I checked out the DMG & Unearthed Arcana's optional HP rules. I don't like those rules as they are, even if I used them as a source of inspiration.
I polled my players about this, and those who helped me test a basic version of it really like it.