The movie is a post apocalyptic science fiction movie. I can only assume that it is set in the future, but it may have been set in the past - it's hard to tell. There is only devastation and barren waste everywhere in the movie.
The story is simple. A man and a boy are wandering the wasteland headed south for no reason except that they are looking for the ocean and hopefully something better than what they left behind. They meet some people and see some screwed up crap and you quickly get the idea that the world is not what we are used to. This isn't "The Book of Eli", where there is a quite thick veil of bullshit over the entire movie. This feels REAL.
Despite its simplicity, each scene is thick with detail and has real impact. The psychology of the situation is evident constantly and the concepts of "hunger", "loneliness", "happiness" and "friendly" are violently twisted into new meanings.
The movie does nothing to explain the apocalypse itself, i.e. what happened or why. It isn't part of the focus. We don't know if there was nuclear holocaust, a disease or aliens, we just know that we're here and it's dire.
In many ways brilliant, but at the same time, depressing and and unsatisfying. You go away impressed at the quality of the acting, directing and cinematography, but don't really know the point of it.