I am excited that Obsidian is doing this, i've liked every game they've made. Sure, they usually make games with technical problems, but they are usually so good in the other respects that those can be overlooked. Plus, they are using the engine that they built for Dungeon Siege 3, and i played it twice with no technical issues so things are looking good for South Park.
They should do alright with this, they are being given a story and the style of game is one they are familiar with....Obsidian isnt that bad, as long as they dont rush it Problem is they usually rush games cutting content and leaving in bugs (which they almost never patch)
I'm not concerned at all. Matt Stone and Trey Parker are overseeing the project and had experience dealing with THQ. I don't think that they'd allow them to release a game that is extremely buggy or inconsistent.