There are elements of science fiction and other unusual things sprinkled throughout the milieu. Here are a listing of some of the alterations to the standard PHB classes you can expect to find. Also, check out the additional feats available.
Barbarians come from two different backgrounds.
One is the more peaceful tribal background, in which the people are ready to defend themselves and their lands, but are not of a particularly warlike culture. These tribes are older, mostly from before the War of Falling Stars. The second background is of the newer raiding barbarian tribes, who live by raiding and conquest. These came about mostly from strong people who were rendered homeless by the War of Falling Stars. These tribes tend to be crafty, wise to the outdoors and the ways of battle, and warlike.