This game has actually 5 games on it (one rated T, the rest M).
HALF LIFE 2: This game is the sequel to Half Life (who would have thought) and, like the first, never leaves the eyes of the protaganist. This can make some moments frustrating for some kids. At the start of the game, you have to run from the aleins that have taken over the planet, and at one point you have to go into an apartment building where some revoultionaries are hiding, and if you have seen Children of Men, it is some what like that but not as suspenseful or bloody. Actually, most of the game is spent running from the aleins until you reach a "safe spot" (safe for a while at least). There are some alein headcrabs that atatach to people's heads and they get some blood on there clothes. When you shoot an alein (they just look like bald humans with gas masks), blood splatters fairly realistally, but still, there is not dismemberment or very much swearing. It is a very good game!!
HALF LIFE 2 EPISODES 1 & 2: pretty much the same as Half Life 2, but different setting.
PORTAL: a few black jokes, nothing overtly racist. There is very very little bloodshed, because it is a first person puzzle game, not exactly a shooter.
TEAM FORTRESS 2: This game is only online, and has pixar cartoon quality graphics. Some people get lit on fire, and they just fall over. Occasionally, your character may get blow to pieces (literally), but it is not very realistic. People cuss online alot, so i usually mute it.
Overall this is an amazing complation. It is not terribly violent, but of course it is suspenseful and some enviornemtal puzzles can be frustrating, but it is still very fun. I think that a thirteen year old should be albe to play this.