Decent enough if unremarkable English-language take on Oliver Hirschbiegels superior Das Experiment, which itself was adapted from a novel (Black Box) which was inspired by a real experiment carried out at Stanford University in 1971. It was funded by the US Navy, and it was abandoned after only six days, when it went tits-up.
The story: a bunch of people are interviewed, and 24 are selected to participate in a social experiment: they are to be coached out to a camera-ed up detention centre, where eight will be selected to play the role of prison guards while the remaining sixteen will adopt the role of prisoners. The experiment is scheduled to last for fourteen days, at the end of which the participants will receive their pay: fourteen grand each. There are rules though, and if any of them are broken a red light will come on signalling the end of the experiment, and no one will be paid: The "prisoners" may not speak to the "guards" unless spoken to first. The "prisoners" are to be given three meals per day, but they must finish their plates. The "Prisoners" must participate in one hour of physical activity every day. If the "prisoners" break any of the rules or play up in any other way, they are to be punished "commensurably" within 30 minutes. There is to be no actual violence committed (odd one, this, as the violence erupts long before the red light eventually comes on. Perhaps those conducting the tests considered the acts "commensurable" to the acts of the prisoners. I dunno). If anyone wants out and quits, it's over for everyone. Anyway, our hero is "prisoner" Adrien Brody (King Kong, Predators) as a pacifist hoping to get some quick cash so's he can follow his latest squeeze out to India where they can "find themselves" and whatnot, and our villain is "guard" Forest Whittaker (Phonebooth, The Last King of Scotland), an initially shy, gently-demeanored man who still lives with his parents, and who befriends Brody at the interview stage, but who allows himself to be sucked utterly into his role as guard, and who is subsequently absolutely corrupted by his absolute "power". Within a matter of days.
The two leads - Oscar winners, both - are clearly slumming it, but they by no means ham it up or chew the scenery. The whole thing is done and dusted in a brisk ninety minutes and as a result there's little time whilst watching to consider the shortcomings or flaws until later (who are these people conducting this experiment, anyway? Why the oppressive, dangerous rule-set? Why don't they leap in as soon as the violence rears up? Why are apparently straight men ready to rape each other like 40-year lifers, when they've only been in there 5 days? Even if the would-be rapist is gay, can't he hold off for a bloody week before resorting to sexual assault? Why is an actor of clearly Hispanic/Mexican descent playing a white supremacist?). It's a decent enough if forgettable way to knock out an hour-and-a-half.