In brief, my preference would be for a system where:
I. You have Hit Points, which represents your ability to keep an attack that hits you from causing a major wound. Any 'hit' makes contact and hurts, but you aren't debilitated. When you run out of HP, you are helpless but conscious. The only actions you can take are to croak out a few words or crawl 5 feet.
II. Critical hits do no extra damage, but instead cause some sort of debilitation. My preference is a list of four options.
--A. Bleed. The character loses HP equal to its level at the end of its turn. If it's at 0 HP, each minute it makes a DC 5 flat save or die. If the attack was with a piercing weapon, increase the save DC to 10.
--B. Daze. The character loses their action and must make a DC 5 flat save at the end of the turn to end the condition. If the attack was with a bludgeoning weapon, increase the DC to 10.
--C. Dent. The attacker damages an object the character was wearing or wielding. Broken weapons count as improvised clubs. Broken armor provides 4 less AC.
--D. Wound. Here we get a bit complicated. There are light wounds and serious wounds; if the target has at least 1 HP after the damage from the crit, it's light and lasts until they take a short rest, but if they have 0 HP it's serious and is permanent until magically healed. Roll a d6 to determine a location. If the attack was with a slashing weapon, roll twice and pick your preferred location.
----1. Eye. Blind for one round, thereafter disadvantage on ranged attack rolls and Perception.
----2. Mouth. Cannot bite or talk at all for one round. Thereafter can only speak at a raspy whisper.
----3. Primary arm. Drop anything held. Thereafter cannot attack with limb or use it to manipulate objects.
----4. Secondary arm. Ditto.
----5. Chest. At the end of any turn you take an action, gain a level of exhaustion. If you take no action on your turn, at the end of the turn exhaustion from this wound goes away.
----6. Leg. Fall prone. Thereafter, it moves at half speed, and whenever it takes damage it falls prone.
III. You regain HP through hit dice and long rests. A 1st level cure wounds spell cures a light wound. A 3rd level cure wounds spell cures a serious one.