There is some blood and guts. Blowing things up. Based on the character you play, you have to learn to kill in a certain way based on the weapons available to that character.
But basically, the game is all kill, kill, kill and it leaves corpses scattered about as you kill and get killed. There is certainly strategy involved, but it’s a “how can I kill them and win” type of strategy. Even if you are playing the version that is basically capture the flag, it’s like capture the flag with guns and bombs and death and blood. Having said that, the violence is pretty cartoonish.
I mean you have a base you defend. With guns and turrets and bombs. You infiltrate the enemy. With guns and turrets and bombs. So if you don’t want to spend your time trying to kill someone else, it’s probably not for you. But there is also strategy and teamwork involved. Since you can talk to other live, there could be cursing—you never know.
Other suggestion: watch the TF2 “trailers”. Go to youtube and look for the DemoMan trailer, Sniper trailer, Soldier trailer, Heavy trailer (worst of the trailers, but also one of the first). They should give you an idea of what you would be getting into. Oh! Also the engineer trailer. If nothing else, they are HIGHLY entertaining, explain the characters a bit, and will let you see the game in a way.
Also: don’t buy TF2 on its own (if it even comes that way). Check out the Orange Box. You’d get Portal (super fun logic game), Half Life 2: Episodes 1 & 2, and TF2.
Last suggestion: try either renting or watching someone play? I watch a friend play ALL THE TIME. I don’t do violence, but it’s still a really fun game to watch. Despite being kill, kill, kill, it’s very cartoonish and the violence isn’t at all realistic looking.