I foolishly watched the film because I studied the book and it was probably the worst mistake I made. A lot of people will be drawn in by the trailer, but unfortunately the trailer holds all the best parts of a film which misses the integral parts of the novel and because of that suspense is ruined somewhat.
While slight name changes are acceptable, what isn't acceptable are the cutting of some of the mainstays of the book. One of the few scenes out of the film which I felt was missing was the library scene in the book where Joe goes to study and is watched by Jed. Also missing out of the film is the part where Clarissas colleague is shot by Jed whilst they're having a meal and the desperation for Joe (a rational man) who wants himself free from Jed and his quest goes in search to find a gun whilst being high.
While Rhys Ifans was great casting for the character of Jed, I felt that Daniel Craig was miscast. I couldn't hear what he said for the mumbling half the time and think there are better actors who could've played the role better.
There are also scenes that try to be too intelligent and could lose the viewer. The scene where they're eating at the table and Clare (Clarissa) becomes angry. There must have been some kind of coding in it, but I couldn't understand which made me as a viewer feel patronised. Because half the scenes are cut from the book and the character of Joe isn't well played, you end up feeling sorry for Jed rather than thinking of him as abnormal. You can see his anger for Jed but in some scenes it looks like he loses it for no reason at all...while these are the signs of a desperate man there isn't enough ammunition to react in that way and so the viewer feels confused.
I loved the book and still do but I feel that the film is a massive letdown.