Intro - Half-Life 2 - Half-Life 2: Episode 1
Half-Life 2: Episode 2 - Portal - Team Fortress 2
Team Fortress 2
is rated "M" for Mature.
Blood and gore: Despite the game's cartoony appearance, it has plenty of blood. It spurts in moderate amounts when you and enemies are shot or hit, and splatters on nearby walls and floors. Blood does linger. It also includes a thing called "gibbing," which means when you use explosives on an enemy, he breaks apart into large, bloody chunks. Though compared to games like Gears of War, the gibbing is more mild, but it's still very present. There is no option to turn off blood in this game.
Intense violence: There are several playable characters in this game, from a scout who is equipped with a baseball bat and shotgun, to a demolitionist, who's equipped with loads of explosive weapons. It does look like a Pixar cartoon, but it's moderately more violent, and as you read from the beginning; it's pretty gory. Add the things listed above and the fact that the only objective is to kill as much as possible, and you get the gist.
Closing comment: There's not much to say, except despite it's "cute" appearance, well, it's not. Because it is an online-only game, with voice chat support, depending on who you play with, there could be loads of language from that specific person. So, seeing as many parents have different viewpoints on online games, at the very minimum, I recommend this game for ages 14+.