I AM LEGEND could have been a bad movie. The people making it could have messed up in many ways. However, they turn the flaws of the story into advantages. Its biggest asset is Will Smith's powerhouse performance. The script is very well-written also. The people making this movie took a big risk. Instead of making it an all-out action thriller with mindless, constant violence, they took the story line and made it, primarily, a tragedy about one man left alone in the world (with some great action pieces on the side).
Parents need to know that this movie is very intense. Even when the action lets up, the emotion doesn't, and several scenes are emotionally draining, whether by fright or sadness. I don't like to include SPOILERS! in my reviews, but for the sake of a well-informed review, I will now. SPOILER! About 50 minutes into the movie, Neville's dog, Sam, becomes infected with the virus. He must strangle her before she becomes a zombie like the rest, and, since the dog is his only companion through the movie, this scene will be too overpowering for kids under 12 at least. END OF SPOILERS. In addition to that emotional scene, there are several others detailing the death of Neville's wife and daughter (helicopter crash). There's no more violence in the movie than there is in, say, a SPIDER-MAN film, but many scenes featuring the zombies will be frightening for kids. The film has a constant feel of desperation and despair, and while I wouldn't call it disturbing, it makes the film NOT for kids.