First thing I need to say is that no, I did not read the book.
Second thing I need to say is that maybe if I had, I would have enjoyed the movie more. Or not, I can't tell now.
Fact is that I feel I totally missed the point of this movie. I won't go to the point of saying it was bad, there were a few good moments, but I don't know, I never got sucked into the film, if that makes sense.
It's the story of a teenager and his guardian on the run of extraterrestrial killers. Said teenager moves from town to town, and is number 4 on the list of teenagers to kill. In his new town, he meets the first girl he falls for, discovers that he has superhuman powers, and that the killers are closer to getting him than he thinks.
What I enjoyed most in this film was watching Timothy Olyphant (let's admit it, who doesn't). Special effects were good too I guess. And the last 20 minutes were a lot more fun than the rest of the movie. For the rest...
This is actually the first film where I thought "this could have actually been made into a good tv show". And then I realized that it already had been used for a tv show, and that was Roswell. No wonder I was not impressed by the movie.
So I'm sad to say I do not recommend, it was unoriginal, boring, some terrible lines, with a few good moments thrown in the middle. Maybe you could try the book?