South Park: The Game was originally set to release in later in 2012 but those plans are being adjusted. THQ announced that they are not going to release South Park: The Game until late 2013 at the earliest.
The project is somewhat unique in that South Park creators Trey Parker and Matt Stone approached developer Obsidian to do the game. The creators have been intimately involved with the development of the game from the beginning, and they will provide all of the voices, just like they do in the show.
Obsidian recently had to lay off some of their employees that were working on South Park: The Game, though it is unknown if those layoffs affected the release time table.