I want to say first off that "I Am Legend" is a very good movie. I want to say further that "I Am Legend" is one of the roughest movies I've ever watched through.
Last week, in "AvP: Requiem", I saw what is could be considered an example of the typical 'monster movie'. It was a 'fantastic' type of movie, and while creepy and scary, it didn't give much of an impression of being realistic in almost any way. The monsters were obviously fictitious, alien, unrealistic, and the characters had that kind of movie-ish unrealistic element to them that is common in such movies.
"...Legend" had a disturbingly realistic edge to it. The story itself is rather fantastic--a virus used to cure cancer mutates and causes people to turn into albino-ish carnivorous bat-like creatures who try to avoid the light. Regular humans are for all that we know when the movie begins down to one man, who along with his dog is living in the wilds of New York City while avoiding being detected by the mutated creatures.
What gives it such a realistic edge is Will Smith. He does a terrific job with a character the is remarkably complex--a scientist who bears the guilt of how wrong his experiment turned out, a man truly alone in a big city, a father and husband who had lost his family, a scientist trying and failing to correct the mistake, a lonely man whose need for company has come down to talking to mannequins and whose family is a dog, and a man who goes over the edge when that dog becomes infected and is killed.
Another thing that made it tough was the creatures. We get the impression early that they are mindless, crazed, without any spark of humanity left in them. That is what Smith's character thinks of them, and then he comes on one that is different--when one of its tribe is captured by the scientist, it acts as if it may actually try to attempt to rescue it, although it was unable to enter the sunlight. Then they set a trap for him, like one he set for them. Then they show signs of having leadership and even communication and an ability to organize. When at one point the scientist says that they have lost all signs of humanity, I think that he knows he's lying to himself.
Much of what Smith does is probably all too realistic--it's not a stretch to think that a man alone for at least two years would become too attached to mannequins, or to his dog, and considering that it was his research that caused the disaster to happen, that he should fight guilt over it and try to remedy it on his own.
The guilt part if tricky, because it is not explicitly said--we don't have a stereotypical breakdown-and-confession, even if it would be with no-one else around. There is the scene where he thinks one remedy fails and he slams some things around, but even that doesn't get out of control. Probably the closest it comes is at the end when he thinks he's found the cure but will be killed by the creatures before he may be able to help them.
But it seems like that guilt is always there in him, pushing him to find the cure and then goading the helplessness he feels into a rash act of revenge, and maybe also having a part in his last act of sacrifice to pass on the cure.
Much has been made of the God-talk in the movie, and it is there, and it is done with respect. A set of too-convenient coincidents are given as signs of divine guidance, and such may well be. Then the fact that Anna's knowledge of the human colony in Vermont (I think that's the right state) is correct only emphasizes the divine guidance.
Of course, it's a work of fiction, but still, it was good to see that the writers didn't leave God out, which would have been understandable in such a bleak story, but that they show His hand even in their troubles.
I really don't know if it's a movie I would want to watch again. It is a very good movie, and I recommend it, but it's harsh and bleak and at times gut-wrenching. It's not a easy movie, not by any stretch, but it is powerful.