In short, aliens have invaded earth, but wear a special skin to appear human. To average people, they appear and sound identical to real humans. The lead character discovers that special sunglasses can show the aliens without their human-like skin. (They look a bit like the aliens from "Mars Attacks".) When wearing the sunglasses, most outdoor adverts are replaced with bland single-party-state-style propaganda encouraging people to consume, work hard, and follow the rules.
I can honestly say that the trailer does no justice for the film. It is much better than the trailer. When I saw first saw this, I was genuinedly spooked. One half of the film is good fun 1980s alien invasion beat 'em up, and the other half is a thoughtful commentary on the age of consumerism.