The premise of this movie is quite obvious, and I wouldn't usually fault it for that. Like much of the "Torture Porn" genre that materialized after the war in Iraq, the inspiration for the story here was Guantánamo Bay and the horrors enacted there, along with the terrible torture footage from Iraq. Where this movie fails a little for me (docked one star) is that they didn't think the audience would be smart enough to make the connection themselves, so there are a couple scenes where you're beat over the head with it.
The ending, bleak as it is, is clearly intended not to allow a sequel, but to further show how the horrors never really end, and how those who perpetrated the actions never seem to pay for what they've done.
The cover art tries to link it with Texas Chainsaw, but that's wholly inappropriate. As for others who have posted reviews complaining about the lack of gore in reference to TCM - I wonder if they've actually watched TCM, which has very little.
Anyway, back to this film. It's gloomy, hopeless, and nasty (but not especially violent or gory). As such it worked.