Yeah, I've done this too. It's similar to the Vitality and Wound Points option from D&D3.5 (I first saw it used in D20 Star Wars, and adapted it from there).

I used a bunch of other homebrew rules with it too, like different weapon types being treated differently (slashing was kinda the baseline, blunt weapons were good at battering people in heavy armor, and piercing weapons were good at getting through armor but only small amounts of lethal damage), HP was the amount of "non-lethal" damage you could take (it added up, and when your HP equaled your ever decreasing Con, you passed out), Armor converted lethal damage to non-lethal (and if you had extra Armor, it would decrease the non-lethal damage taken). I had a Bleed score, and anytime you took lethal damage (lethal meaning damage to your Con not HP), it would increase your Bleed by 1 (or more depending on the weapon used). Every round you were bleeding, you have to make a Con check to avoid going into shock (going unconcious), which gets harder and harder the more lethal damage you take. I also had a Block action, and how it was used, was if you were attacked and hadn't acted in the round yet, you could forfeit your action to Block, which was an opposed attack roll (usually with a bonus) that could cancel out your opponents attack. I also let you forfeit your movement to move with an opponent (to better simulate two duelists maneuvering around each other). I had initiative rolled every round, so it created a really nice back and forth of blocking or attacking.

Yeah, with all these extra rules combat rounds took a little longer, but since there was rarely more than one or two rounds of combat (with everyone dead or bleeding out by then), combat actually ended up being quicker overall.

I loved my deadly-as-hell version of D&D, but only a few people ever wanted to play it with me.

Feel free to shoot me a PM if you want to talk about it more.