As I sit here not being caught up by the grace of God, I find myself wondering what a post-rapture world would be like.
As I understand it, anybody left behind is a sinner, and will not be saved, and a good proportion of the population will have been swept up and have vanished whilst a multitude of natural disasters occur across the globe.
The dead may also rise. I'm not too clear on this point.
So, the players would be sinners/non-believers who have to survive the wrath of God in a depleted world.
Society will have totally broken down, with people finding strong religion when its too late or embracing their damnation, both leading to social and physical conflict.
There may also be zombies.
As an additional touch, you could populate the skies with the hovering forms of the blessed, watching the world being destroyed and reborn from their vantage point.
You could also throw in further Christian mythology, and gear up for the last battle between Heaven and Hell, with Angels, Demons and the souls of the damned and the saved.
With its Morality system, Virtues and Vices, the World of Darkness could carry this setting idea quite well.