I cannot remember when exactly I heard of I am Legend, but I know that I immediately wanted to read it (I want to say that it was from some 1970s Hugo award-winning derivative, but I think this origin is unlikely). I am reasonably sure that the novel's Wikipedia page has spoilers, but I have never read it (just to make certain). When I saw the preview trailer (twice!) for the movie with Will Smith earlier this year, I knew that I would have to read the book before the film was released.
Normally when I read a book and I know a feature film is upcoming, I am hopeful that the movie will not only adequately transform the book's words into images, but will enhance it. With I am Legend, I want exactly the opposite. From what I have seen from the extended trailers shown during the World Series, the film may stray substantially from the book. This would be a Very Good Thing. Read on for spoilers about the book, which I do not think you should read anyway.
The main character in I am Legend is Robert Neville. In what has become science-fiction cliché, he is the only human left on Earth. Everyone else is either dead, or has become a vampire. Neville spends his nights barricaded into a fortress-like home, but is able to move freely during the days.
While I realize that the book was groundbreaking back in 1954, there are still enough unreasonable plot elements that had me rolling my eyes. For example:
To the vampires, Neville is a serial killer, a monster that comes during the daylight hours and kills them mercilessly.
To them he was some terrible scourge they had never seen, a scourge even worse than the disease they had come to live with. He was an invisible specter who had left for evidence of his existence the bloodless bodies of their loved ones.