I saw Children of Men a year ago, but didn't give much thought on it. Until recently, I watched Zizek's brief commentary (as part of the DVD special features) and realized I'd overlooked a key element in the movie. Zizek points out the importance of reading the background which reveals the oppressive social dimension. This is very true, since if we erased all the messages conveyed by the background, the film would become a superficial sci-fi like most Hollywood sci-fi movies.
I can't help recalling Terry Gilliam's classic Brazil, a combo of sci-fi, comedy and political satire. The difference is that: in Brazil the social/political struggle is demonstrated in the foreground together with story-telling, whereas in Children of Men most of the political events and details are placed in the background.