I still remember South Park on the N64 by Iguana (of Turok fame); it was a good idea and had an interesting story and original voice acting, but was terribly marred by its bad game design. Draw distances were absolutely absurd, movement was painful, and it really wasn't worth suffering through just to find out what happens to the characters. I didn't keep up with future South Park games, but I don't believe they made an uphill climb.
In more capable hands South Park could have been a much better game, and I think of Obsidian as a pretty capable team, especially when dealing with established IPs (KotoR 2 and New Vegas, to name two). I'm certainly curious to see how they handle this, though I doubt that it'd be a day-one purchase for me; I lost interest in South Park a long time ago.