Thirded. I really like it, but I also like South Park. I think the game is genuinely funny on its own, but it's also clearly made with the assumption that you know these characters, the world, the style of humor, and are at least somewhat fluent with the many, many references to the show that are in it.
It's a fantastic game for fans of South Park and a funny, though kind of confusing light RPG for everyone else.