Two years have passed since the defeat of Sephiroth, but the world is yet again at unease. We know of something called the Star-Scar Syndrome, which plagues the human race. One theory is that this is one of the effects Holy has had on the planet -- wanting to wipe out the humans, who causes nothing but harm to the planet. But no official comment has been made on that.
Cloud obviously has the main role in the movie, but the trailer gives the impression that he's yet again a loner. This might be misleading, though, since the developers haven't had time to finish any others of the characters.