This movie clocks at around one hour, and accomplishes what most modern thrillers struggle to do in twice the time. It gets to the point pretty quickly, but gives a straight, well defined portrait of the main characters without using any "super obvious" scenes to do that. While in the process it actually utilizes pretty much every cliché of the whole "kidnapping" scenario of horror movies (like for example "the hills have eyes" by the late Wes Craven)but in the best way possible. It manages to hold the viewer at the edge of the seat for every single second, surprisingly without ever feeling predictable.
The cinematography and imagery is appropriately beautiful. The worn out color palette fits the ugly urban location perfectly and helps in creating tension throughout the movie. You could even say that (taking into consideration the extremely limited cast) even the weather and the building themselves are supporting characters in the film.
What is really worth mentioning is that this is one more Jaume Balagueró film that breaks the mould of American horror films by having the story placed in an apartments. With the obvious exception of Roman Polanski's "Apartment" trilogy, most American thrillers are set into suburban locations and big, very big houses. Although these houses are very scary (mostly due to their abundance of entry points, making the villains job much easier) this is not very realistic considering more than most people worldwide live in blocks of flats and cant' actually relate to that "50's America" scenery.
Top up all of the above with a great psychological/social study on people who are obsessed with other peoples lives and you've got an excellent, disturbing and actually very "thrilling" thriller. The only drawback I can think for this movie, is (as noted by most reviewers) the main characters lack of decisiveness at points, which, kind of feels like a mechanism for the film to go on.
