I've never seen South Park. It's one of my to-do things (along with watching The Sopranos, The Wire and growing up a bit). But I know that it is irreverent, profane and takes no prisoners. That's plenty enough preparation for this.
It's not as clever as it would like to think. It says that America being "the world's policeman" rides roughshod over everything in its own interest, that lefty Hollywood stars are a self-important, uninformed and gushing and that Jerry Bruckheimer-style blockbusters are predictable and stilted. This isn't an ambitious movie- how many soft targets do you want to hit? It's not enough to take the piss out of Michael Moore if you're basically doing the same schtick.
But it is sporadically funny, well-made and the songs are worth hearing at least once. 4/10.
