The Purge
On the one night a year the government allows violence, a family finds themselves terrorised in the home they thought they’d made safe.
The Purge tries to be both social commentary and a horror movie about home invasion and fails at both. It could have been much better, it just doesn’t know what it wants to be when it grows up. You can certainly combine genres very successfully: Evil Dead II and Little Shop of Horrors are both successful horror/comedies, for example. Those films use balance, intermixing one with the other. The Purge, although at first glance seems like it might, does not and it suffers for it, not helped by a dubious premise that is never fully developed. What they’re trying to achieve by using the extremes shown and discussed in the story needs a lot more background given to us before it can be believable. TVTropes has a more in-depth explanation of the problems on the film’s page under the Artistic License - Economics and Hollywood Psych sections.
Unfortunately, The Purge doesn’t follow up on its promise of social commentary mixed with horror, turning into a pretty standard home invasion horror flick with the obligatory twist ending. None of the characters are developed enough to give them any depth, and as a result The Purge fails to become what it clearly wants to be.