A respectable blend of drama and horror, using strengths of both but also succumbing occasionally to the weaknesses.

Suspense is present from the very beginning, building to an exciting and unexpected climax, unfortunately falling a bit flat afterward. In fact, the last 30 seconds of the film somewhat blemish the drama of the story as a whole, mostly because the ending touches on a relationship that was hardly explored and not at all significant through the rest of the film, partly because of the focus on the very thing that makes this movie good: the constant twists and turns in the story. This also leads to some ideas that are passable but don't make nearly as much sense as they're supposed to; particularly the whole "people who aren't seen"/"There was no man with her (Sara)"/"Don't look at me!" motif. I still don't get it, but it has little impact on the story anyway.

I believe the entirety of the story could have used some fine tuning, and run time could have been trimmed by 10 to 15 minutes... But overall it's engaging, well acted, and sets an excellent and fitting mood visually. Thrillers that can't project the protagonist's experience to the viewer fail horribly... this movie does an outstanding job providing a sense of confinement that fits the title character's world, and this is where its greatest strength lies.

Although character relationships are a bit thin and suspense doesn't hit many high notes, this is a fairly exciting thrill ride and a good effort all around. One last thing, I would recommend watching it without distraction... the mood is more visual and in the flow of the story than it is intellectual or suspenseful, and it's easy to lose interest if you step away for a few minutes.