If you are looking for a first person shooter, that isn't actually very violent, then there would be two games that I would suggest-Portal and Mirror's Edge.
The game is big, expansive, and cheap(at least for the PC[20$!]). The story is so good it could even be put into a movie!
The gameplay is unique, and even though there is violence, the least of it is what Faith dishes out(at least while you're playing as her.)Most of it is by The Blues and some other characters.
Another thing that I found saddening is that the only blood appears in cutscenes,(seeing people that were murdered or be murder) and not when you actually shoot people. But, when you are shot, a red splat(you guessed it)appearson the screen where you just were shot.
The only other violence that I would say is that when Faith gets killed in a certain manner, she falls on the ground, lifts up her hand, then drops it.
The REAL reason that this game is rated T is because of all of the SWEARING. Yes, ALL of the SWEARING. Da-n, Sh-t, A-s, Hell, plus some Screwed and others that I am forgetting.
However, the worst part would be that most of the characters swear.
Overall, this game is one to buy. Oh yeah-If you can, get it for the Xbox or PS3, cause physics don't work on the PC.