Hell, Doom? You guys ever play the Tom Clancy Rainbow series? With modification they can be made to allow play with any gun currently in Jane's database, depending on who you get your mod from. Decent realism too, but aimed towards SWAT style operations.
Further than that, the two latest I've been playing are one called Operation Flashpoint- a Cold-War era US-Soviet conflict on a Falklands size/type theater. Not only are the weapons realistic, as per limitations, sighting, breathing, mag changes, ammo you can carry, but you've got full ability to interact with your environment, able to talk to other players and even take weapons from dead guys. My favourite scenerio to play is one where you have a tank crew in a village, the crew is dismounted and in a defensive formation around the tank. You select hunters with shotguns, wipe the crew out, and steal the tank. (Also avaliable are Hinds, Apache, Cobras, Mil-8s, etc etc...).
The kills are pretty close to 'nightly news' kinds of reality. Enemies take, quite often, more than one round to drop, friends and squadmates can get wounded, and are very loud about it. Although I've yet to see guts (computer is too slow to play on high-rez), there is a fair amount of blood in the game.
The other game I'm currently playing is called Ghost Recon, its another Clancy small unit game, but this time not in cities, against Terrs. but out on the battlefield. It too has fairly realistic kill effects.
I've grown up on computers, most of my games until recently have been combat flight simulators or tank games. Destroying a KV-6 on the outskirts of Moscow with a Panzer isnt as desensitizing as one would assume wiping out a whole group of Soviet Spetznas (or GIs... sometimes its so fun to be bad) with a SAW, but even as I've been playing these games since, well, the early 90s (Was what, 14 when doom came out? I think...) I still get a certain lump in my throat when I've had to kill things in the past, and feel a little bit guilty. Even if it was just a rat going throgh my trash, or a rabbit in the back yard with a pellet gun that I later skinned and ate. Blood, others, not my own, makes me nauseous still, and I cant stand to see anyone, even if they were Adolph Hitler, in pain.