One of my old favorites, especially when I was really in a foul mood was, Soldier of Fortune, and Later Soldier of Fortune II. Excellent graphics and when you get a headshot the guys head expleded, a gut shot, and guts spilled to the floor and a legshot and he'll be screaming and hopping on one leg.
The video on this page, gives a good show of what I mean about what these games are like....
And here is one reason sometimes it's hard for me to stomach, "bleeding heart liberals". Many of them won't let their boys have toy guns, even squirt guns. Violence is a part of human nature, and if you don't abuse a child and teach him that its not ok to use violence to get his way, or to bully others, or essentially any time except, appropriate times (ie soldiers at war, self defense, and defense of another who cannot defend themself), than he should be ok.
Personally if my 8 year old (I don't have one, but if I did) wanted to play something like "Medal of Honor", or one of those pussy games where you gun down the enemy and its sanitary (they just fall limp with no blood), I would not allow it. I'd go pick him up a copy of Soldier of Fortune, and have a talk with him about it and say have fun dude, this game is AWESOME. I'd want him to know if he ever serves his contry and has to go to war, that that would be the only time it's really appropriate to do this kind of thing in real life.
I personally would much rather have a realistic depiction for my son, than let him get the idea that killing is just good clean fun. I see no big issue with exercising this natural part of human nature, so long as you do it in a way that is, safe and appropriate, and a pretend game is fine by me.