A couple spending a romantic weekend together by the lake have an unpleasant brush with some local teenage cretins. It starts harmless enough, with an awkward argument on the beach, but soon things go too far and the couple find themselves fighting for their lives against the punks' sociopathic leader.
Eden Lake started off strong, but stumbled somewhere in the middle before collapsing on itself by the end. The opening act or so had me hooked. The couple was convincing and sympathetic, and the early confrontations with the teenagers were effectively unsettling. It's horror right out of real life: you ask some asshole to turn his music down, they respond standoffishly, there's a vague threat of violence and you feel unsettled. We've all been there.
It's when things escalated that the film started to lose me a little. The violence perpetrated by the teens goes too far. I don't mean that in a moralist sense, as if I was offended by the movie. And I don't mean that it's not plausible that seemingly regular teenagers could be capable of such atrocities. What I don't accept is the manner and speed in which the violence escalates, the lack of hesitation shown by the lead creep, and the relative ease with which he convinces his nervous cohorts. To the filmmakers' credit, they try to show how he bullies and scares the other teens into following his lead, but the execution is rushed and it rings false.
Still, the middle segment of the movie remained competent and engaging, and I could have accepted Eden Lake as an effective, if too contrived, thriller. Then the ending killed it. The final act asks us to accept the exact same plot twist three times in a row (someone offers their help to the couple, but it turns out they have some sort of connection to the teens!), each one worse than the last. The final scene really turned me off, in which the parents of the teens turn out to be just as vicious as their offspring.
I have no problem with a horror film ending in misery and cynicism, if that's its goal, but it has to earn that sort of conclusion, not fabricate it. I'm sure the filmmakers are trying to make some sort of statement about how the cruelty was taught to the children by their families, and that's fine, but the final moments rang so false to me, so forced and lacking in credibility, that it tainted the whole experience.