South Park: The Game will be the new kid in town, and the main struggle will be to fit in and be accepted (See? South Park really is a public-programming after-school show, mom). Characters will be completely customizable and Cartman will help players choose their class -- wizard, paladin, adventurer, rogue or another, unannounced class made up by Cartman.
The story will begin with players joining a live-action RPG with neighborhood kids, which will then turn into a real adventure. The combat system will mirror Paper Mario, weapon augmentation will draw from Final Fantasy's Materia, and the levels are all illustrated and animated by hand, in a completely 2D format, devoid of any real-life hamsters. Parker and Stone say there will be a summoning system, but that they can't talk about it yet.
And, most shocking of all, Parker and Stone say the game will be funny. NeoGAF has a nice summary of the article right here.