Someone over at NeoGAF apparently got hold of the South Park edition of Game Informer and has posted up relevant details. These include:

- You play as a silent protagonist. A new kid in town who must work to fit in. - It’s the first South Park game Stone and Parker have actively participated in and written the script for. - Obsidian is using the Dungeon Siege III engine, there will be five classes (wizard, paladin, adventurer, rogue, and a fifth unannounced class). - Apparently “elements of the combat system are like Paper Mario and the Mario & Luigi games”. So it’s an RPG map with turn-based encounters.

Sounds like a peculiar blend! But that could be for the best. Plenty more spoilery details through the link.