A cross between "Death Race 2000," a Twilight Zone episode known as "The Shelter", 2010's "The Strangers", and 2013's "The Hunger Games," (with some "Hostel" thrown in for good measure), "The Purge" is pretty solid for a low budget sci-fi film but surprisingly isn't that memorable given its premise.
Set in a near future where the U.S. has just recovered from a massive Depression, and keeps crime low by holding a 12-hour "purge" every year, where murder is essentially legal. It's a day when you can get back at anyone you hate without any consequences -- except for the possibility of being killed yourself. Rich people invest heavily in security systems and stay indoors. But some of them go out to kill the poor.
Ethan Hawke (who, after this and "Sinister," appears to be making a career out of playing flawed father characters in horror films) is a salesman of those security systems who drives home the afternoon before the purge, locks his family up and gets ready for a quiet night at home with the wife and kids while the world goes to hell outside. But after closing his household up to the outside world two things go wrong: His daughter's boyfriend shows up, after having snuck in. And his younger son rescues a homeless guy being chased by homicidal young Republicans by giving him sanctuary in their fortress home.
Needless to say, the college Republicans decide to target the family. Led by an aryan, long-haired frat boy type (the incredible Rhys Wakefield), the group dons scary smiley masks a la "The Strangers" and stage an assault on the well fortified home.
Naturally, as the night wears on, some of the bad guys get inside and Hawke and family are forced to revert to their brutal, animal natures to survive. The kind of stuff that always happens in these fear films.
While taking on social and racial issues, "The Purge" unfortunately pulls most of its punches and reverts to standard horror-revenge cliches, ultimately degenerating into the violent bloodbath that it is purportedly condemning.
Such a massive hit that a sequel followed just one year later.