The DVD featurette suggests that this film was inspired by a single event in the writer/director's life. In my experience, that tends to be a problem because it can produce somewhat unsatisfying movies which attempt (usually unsuccessfully) to build a full story around that event.
In this case, what you get is a horror movie with a good cast playing characters who each have a single, predetermined contribution to make to the story (I.e. a grisly death). This is a good illustration of the fundamental problem: unless you've never seen a horror movie before, there aren't any real surprises (and the shocks are gruesome but not surprising - what else did we think would happen to Peripheral Character X?).
Most infuriatingly, this movie uses creepy music and gently pulsating graphical effects to tell you when to be unsettled. This is an example of an increasingly common movie device: perhaps the filmmakers assumed that the audience was not smart enough to understand which parts of the movie to be scared by without signposting them?