If you haven't checked out the original Disciples, then make sure to soon. The game's setting is the same fantasy world with the same four opposing gods, two good and two evil. Each of the four factions has vastly different units, not only in appearance but also in use. For example, the Empire has clerics that heal friendly units, while the Hordes have a witch that transforms enemies into imps. The resources in Disciples II are the same from the original.
Gold is the only currency, and the different forms of mana can also be harvested.
The Empire's ground is grass, for example, while the Hordes have dry, cracked earth. The Legion's ground is volcanic and the Mountain Clans have snow. While your ground covers a resource area, each turn you get more of that resource. Gold is used to purchase units, upgrade towns, and build upgrade structures at the capitol, while the various mana are used to research and cast spells. Speaking of upgrading, the capitol city of a faction can have buildings built within that allow different units to upgrade along a path as they gain experience.