At the expense of of making myself cannon fodder for the exact attitude that Trey and Matt will be targeting for satire, here's my take on some things that I think we can reasonably expect from the South Park RPG:
Loads of humor -- written by Matt and Trey.
Open and explorable South Park world
Limited C&C -- it will primarily be a satire on games like the Final Fantasy series, but might also draw from other popular RPG series' like the Elder Scrolls. We know C&C is generally not the strongest elements of these games.
Decent length -- we might not get 50 hours worth, but I would imagine at least 20, considering they aim to satirize the "bombastic" nature of RPG's.