Codemasters have released more details
about Overlord, described as a "twisted action RPG" for the PC and Xbox 360:
In Overlord(tm), players begin the game as a wonderfully despotic character complete with a small team of loyal minion side-kicks. As areas of the kingdom are conquered, the Overlord grows in might to become the supremely powerful force, equipped with devastating spells and a devoted minion horde at his command. It's like character building on steroids...
There's a trailer
showcasing the action. There are some more details in the press release, and we've got some screenshots