Okay, so they didn't film the book. I knew that going in, but I was prepared to enjoy the special effects, which I did. Digression: The first movie I remember having seen that used a deserted New York as a backdrop was long ago. It was The World, the Flesh, and the Devil, and it starred Harry Belafonte and Inger Stevens. It impressed the heck out of me. End of digression. I was impressed by the deserted city in this movie, too. There are some great shots of the empty streets filled with abandoned cars and the wrecked bridges you can see in the poster.
The mutants were okay, even if they weren't the vampires of the novel, but only okay. Some of the CGI work was pretty lousy. Will Smith is good, though, and so is the dog.
The movie's ending sure isn't the book's ending, and I didn't much care for it. In fact, the whole second half of the movie seemed rushed, as if they'd just decided, what the heck, let's get it over with.