Mechwarrior 3rd Ed. (Battletech RPG) is pretty hardcore when it comes to damage and survival rates if you get hit...mostly because in the Battletech universe, Medical science has taken a backburner to Weapons Tech, which means that their Med Tech isn't an awful lot better than what we have today (in RL). If you get shot, it takes months to heal properly and until that time, you're taking penalties for the wound.

As far as the ruleset goes, it's one of the more detailed and realistic systems I've seen...there is little to no abstraction (like AC or HP) and it lists modifiers for a great many circumstantial situations (from called shots to varying light levels in combat and from fatigue levels to straight difficulty in other tasks).

Many people might find it too detailed, but as far as I'm concerned it's one of the best RP systems I've encountered, simply because it models reality so well (as far as you can in a Sci-Fi setting), yet maintains the potential for that fantastic element that lets you perform the heroic.