From what I can tell from the movie trailer it seems to follow the book. Will Smith's character's name is Robert Neville, the survivor of a virus that has wiped out most of the population of the earth, including his family. The virus transforms all that contact it into vampires, ("vampires" is not used in the movie though). In the book, Neville survives due to his immunity to the virus. A temporary cure is created, allowing living people who have the virus to walk in daylight, and even eventually achieve a normal lifestyle. To them, Neville is on par with the vampire's who strive to kill the new societies founders. The book's location is Los Angeles, but the movie takes place in New York. As far as Robert knows, he is the only uninfected person in New York, and possibly the world. He spends his time trying to make contact with other survivors, working on a cure to the virus using his blood and, of course, killing vampires, dead and living.
I Am Legend is the third movie based on the 1954 Richard Matheson book of the same name (Matheson also penned Nightmare at 20,000 feet.) The first movie was called "The Last Man on Earth" starring Vincent Price, it was filmed in Italy in 1964.
This second movie based on the book was the 1971 classic movie "The Omega Man" that starred Charlton Heston as Robert Neville and Anthony Zerbe as Matthias the leader of the infected people that do their best to kill Charlton Heston due to the fact that Neville represents everything wrong that used to be before the virus.
I read that this is a serious attempt to make a good movie based on the book, and that you will most likely not see any reference to Omega Man or The Last Man on Earth
