GameSpy posted today a preview straight from GenCon, and here's the lowdown:

Fallen Earth takes place in the area surrounding the Hoover Dam. It's the 22nd century and there's not a whole lot left of human civilization. The world was brought low by a disease called the Shiva virus. The disease begins in Southeast Asia, mutating so fast that the world's scientists and doctors can't find a cure. As millions and then billions of people worldwide begin dying, civilization collapses, in some cases triggering nuclear exchanges between old rivals who each believe that their enemies unleashed the plague. In 2154, the present, all that's left of "civilization" is a ragged collection of city-states in the Grand Canyon region. It's an area crawling with mutated animals, mutated people, and mutually hostile tribes.

Read full preview here.