Any resemblance between this film and the novel of the same name is entirely coincidental. Perhaps the blurb should be clear this is really a remake of 1971's The Omega Man. It means anyone hoping some of the beauty of Richard Matheson's original making its way into this is going to be disappointed. There's not even any vampires! The following does include some spoilers, so be warned.
This isn't to say I Am Legend is a bad film, taken on its own terms. The premise is simple. A new cancer treatment engineered by a Dr Krippin (ho, ho) is going through medical trials with a 100% cure rate. Unfortunately, the viral agent used mutates into a highly infectious pathogen that ends up killing 90% of those infected. It turns out only 1% of the human race is immune, but the other 9% have regressed to hyperactive flesh-eaters that hunt and feast on survivors. Enter Lt. Colonel Robert Neville (Will Smith), who elected to stay behind on Manhattan Island after it was quarantined, to try and find a cure using his own blood as a basis. By day he forages through the city for supplies while the infected sleep, and by night he withdraws to his fortified compound.
The result is a film that romps through its 100 minutes or so. Its not taxing on the brain as, with most big budget Hollywood productions, it allows the CGI and cinematography to create a real spectacle that dazzles rather than provoke deep thoughts. The scenes of Will Smith racing around a deserted and weed-strewn New York are breathtaking, though lacking the menace of the London of 28 Days Later. Generally speaking, the infected lack the horror of the aforementioned film too. Blood-lusting running zombies coming for you are scary, but not bald and grey men churned out of computers. Still, the pace of the film and the appeal of the plot make it entertaining enough, and it is a must for anyone who (like me) find last man on Earth-type scenarios compelling.
I Am Legend has been read as s War on Terror allegory. For instance, this reviewer notes
Western medicine takes a virus (a bad thing) and manipulates it so that it can fight cancer (a worse thing). Sort of like Western military forces arming jihadists (which they regard as a bad thing) so that they'll fight communists (which they regard as a worse thing). And then the built-up virus - the bad thing - mutates into something much worse than cancer, and it turns on its creators. And this starts where? That's right: In New York, which everyone in the movie keeps calling Ground Zero. And some poor schmoe who didn't start the problem has to try and fix it. But even if he comes up with a cure ... they [the infected] are just going to keep coming ... destroying the civilised world and - here's the kicker - either killing everyone they come into contact with or converting them into monsters just like themselves. And the only solution is to shoot them dead - or withdraw behind metal walls, into a fortress-like homeland.
There is something to this argument, but that is not all that can be said. I would suggest I Am Legend says deeply conservative things about gender relations. The originator of the virus, Dr Krippin, is a woman. And just look, when a woman assumes a position of responsibility she happens to bring the human race to the edge of extinction. She obviously didn't know her limits, so it falls to a man to clear up her mess. In the evacuation of Manhattan, it's a faulty scan of his wife that leads to their rescue helicopter taking off late, leading to a mid-air collision and the death of Neville's family. At one point his dog, Sam (later revealed to be short for Samantha), disappears into a dark building full of infected - Will Smith has to rescue her and escapes narrowly with his life. Of all the infected to rampage through the film, who does Will Smith capture for his medical experiments? You guessed it, the only discernible woman from among their anonymous grey mass. When a couple of other survivors turn up (Anna, and a young boy, Ethan), she confesses it was a message from the great patriarch in the sky that brought them to New York and was spurring her on to a survivor's colony in Vermont. And of course, the agency of one man delivers the human race from the grim fate awaiting it. The film has nothing positive to say about women at all: they have to be subject to supervision by men, otherwise harm comes to themselves and/or others.
I Am Legend is a stunning example of 21st century movie making. But as a piece of social commentary, its message is stuck in the 19th.