The film version of "The Ruins" is a classic example of "not as good as the book". Unfortunately, the book wasn't that great, either. By isolating the story in one small geographic area (really, just one "ruin"), writer Scott Smith increases the despair of his characters, but also limits where the narrative can go. The main antagonist lacks the sinister, deliberate quality that it had in the book, making it seem somewhat more incidental than the secondary antagonist(s). Without giving too much away, Smith never explains the theory of "why" they are trapped, as in the book, so it feels less satisfying. Ultimately, it gets the Hollywood treatment, with a different ending, the omission of a crucial character (his lines/actions are given to other members of an already large protagonistic cast), and a final feeling of "that's it?".