I recently spoke with an American who said that she didn't really enjoy the movie. On reflection I mentioned to her that (while it had a solid and serious message) the film was filled with jokes that had me rolling in my seat. The reason why she never found it so was because the jokes are largely cultural and based on events in our history and would thus be difficult for non-South African's to catch. Give it a try though, watch the movie and leave a comment to tell me what you thought about it.
Oh, just a side note, Johannesburg is nothing like how it's represented in the movie. ;)