I've of course played D&D with hit points, but found the massive damage rule to have been an after-though kludge.
As a Hero player for many years, I liked the split Body & Stun setup, which enabled people to be ko'd, or to be still fighting and bleeding to death, seemed to cover the full range of effects, which is appealing. (I.e., ko'ing people & subdual damage are yet another kludge on D&D hit point systems.)
I long liked d6 Star Wars' save system (liked the system in general, actually), and really like the M&M save system as well - a single blow can k.o. you or disable you. (Hero *could*, but it was really unlikely, and you had issues with small guns not being able to head-shot kill people.) My only issue with the M&M save system is that you can't "accidentally" get a lethal effect - even in Hero, if your regular damage martial artist hit somebody, they could roll a high body result and get that sort of effect.
After playing all these systems, I want a system that does the following:
1. enables a single blow to ko/disable (or kill, depending on the genre) a foe, i.e., no peasant with a longsword against a 5th level D&D fighter situations or Hero small hand-gun shot to the head situations. This requirement seems to eliminate "hit points" types of systems, because they are hard to line up with weapons' damage.
2. allows a range of results, from injury to disabling, stunning to ko'ing, but not in great detail, i.e., I'm not worried about if your wound was to the outer pinky or lower thigh, and whether a bone broke (those may be good for a few narrow games, but I'm looking for a fast system to play).
3. does not pigeon-hole an attack to *only* doing lethal or stun damage - tazers can kill people, and so can a boxer's fist, whether he means to or not. I'd like to see a good way to modify M&M's system to take this into account.
4. has minimal recordkeeping (e.g., vitality points, and hit points, and wounds, or whatever seem like more than I want to bother with).
5. doesn't feel like a kludge to get the above effects.
Basically it seems like the M&M system, with some modification to reflect that a bullet could k.o. you without killing you or a tazer or fist could kill you and not just k.o. you. I think that system would cover all the permutations most want, except in a really gritty realistic game where limbs are severed, etc., and could handle those effects as well as an add-on (e.g., hit location chart for the wound location, if injured there, then X penalty (e.g., in the hand, -2 to attacks or skills using that hand until healed), if disabled there, then Y penalty, plus potential long-term damage or severed part, etc.).