The story is about a strange occurrence that causes people to temporarily become disorientated, pause mid-step, then take actions to do themselves in. Not sure whether this is a terrorist attack or some strange disease spreading people begin to flee the major cities. Mark Wahlberg and his wife are two of these people. They end up on foot, running from an unknown attacker along with the daughter of Wahlberg's teaching associate.
What this movie lacks is also probably it's strongest point. For the first time Shyamalan doesn't try to catch the audience with an "ah-ha" moment. The source of the event is suggested fairly early on in the film and we gain more information as the story progresses. But by taking away the tension of anticipating a twist, he allows the audience time to ponder on the implications of the event itself. There is very limited information on the event and, without an obvious external trigger, the whole film has a pervasive sense of dread that we can never quite escape from. Even though none of the characters SAY it, you can almost hear their rationale as they realize that they're acting on the best information possible, even though it is limited and will probably lead them to their deaths.
The film ends on a bit of a cliche "everything's better in happy-land now" type note, but given that the whole film we're waiting to find out what happens LATER I think the "content moment followed by suggestion of impending doom" was about the best one could hope for. A lot of people will be disappointed in this film based solely on the fact that it's by Shyamalan. But I think that if you watched it without that qualifier, you might actually enjoy the movie. No it's not The Sixth Sense, but it's a decent movie in it's own right.