Poorly Structured; Writers AWOL -- Spoiler
The long lethargic first act of this film is rather good: Evocatively shot, nicely observed, well performed. Then the silences and simmering grievances give way to a flurry of frantic "I Know Who You Are And I Saw What You Did" plotting, "Last Summer" style jealousy and a major relationship that develops completely off-screen. The rest is just plain silly and the denouement completely unearned. It is also emotionally and developmentally counter-intuitive to what has preceded it with characters behaving the way the writers need them to behave solely so they can slap a nasty ending on the film.
For example: why in the world would Mark lead his friends into the woods to dig up the body that he killed? At no point is it at all evident (visually, psychologically, schematically) that the character wants to 'confess'.