The fellows at NeoGAF enumerated the details in the feature story. For those of you who wish to have a fresh experience, be warned - there are spoilers in the content below.
According to the NeoGAF post, the player avatar will be silent, thanks in part to Parker expressing a preference to nonspeaking player characters in RPGs. However, the PC will be fully customizable, and owns a smartphone that will act as the game menu, featuring a Facebook-like app that keeps track of the number of friends the player makes and their standing among the various factions in town. Considering Obsidian’s past, like Alpha Protocol, the mutability of the story is probably high.
There will be five classes, which include the RPG standards, the wizard, paladin, adventurer and rogue. The fifth class is an invention of Cartman’s. Other standard RPG tropes include critical hits, cash rewards, experience, and consumables, and since this is a South Park game, expect a lot of fourth wall-breaking comments and asides about roleplaying conventions. There will be no unskippable cutscenes as well.
The game looks and sounds exactly like an episode, using the Dungeon Siege III engine, as well as a dynamic lip-syncing tool to accommodate changes to the script. Parker and Stone gave Obsidian fifteen years worth of assets used during the show and a detailed list of approved textures and colors. The player will play as the new kid in town. The overriding theme of the game is about the player trying to fit in with the neighborhood kids. It evolves into a grand arcing adventure.
As for as combat and actual gameplay, players who are familiar with Fable II and III, Paper Mario and the Mario & Luigi games will feel instantly at home, with timed X button melee attacks; pressing it in well-timed succession will result in multiple hits, with timed inputs for defense to reduce damage. The game will also feature dynamic camera angles during combat. On the overmap, enemies will be visible on the map much like JRPGs like Blue Dragon.
The game will feature melee and ranged weapons, and there will be a Final Fantasy Materia-like system in the game to augment weapons with various abilities like fire, poison, and electricity. There will also be a Summon System but the devs were not able to talk about it. However, there are collectibles to look for in the environments, and some appear throughout the game while other are in specific areas. One example of a collectible given in the article is a Chinpokomon doll and a magazine.
The article also featured an interview with Parker and Stone, who discussed their input with the game, nixing a giant rat monster encounter because it ”wasn’t South Park”, instead having them include a quest to get Kung Pao Chicken from City Wok, to readjust Obsidian’s focus.
South Park: The Game is being developed for PC, Xbox 360 and PlayStation 3.