I can't say whether it works in the book, but in the film the lack of children being born works as a metaphor for the looming doom of the human race. It means you look on each scene - graffiti on a bridge, a stand of pine trees - and think 'in fifty years there will be nobody to see this'. Like might happen in real life. That's what SF should be like - make you rub your eyes and say 'Oh, this is the world I've been living in without noticing it'. It's like 'Wakey wakey!' Although I don't think this particular plague of infertility will happen, almost everything else in the film is a plausible extrapolation of the present day. It's not about prediction, it's about seeing what we are.
Apart from that, it's funny sometimes, many of the jokes happen in the background, like the pigs over Battersea power station. Michael Caine is not only in it, he plays Steve Bell from the Guardian, gone all old and mellow. More or less anyway. Smashing. A superb little performance.
It's hard to explain one of the most important, and subtle, virtues of this film without giving anything away, but I think I can do it without any spoiler. This is an action film to a strong degree - it's like Die Hard level action (though completely different action) - but unlike Bruce Willis, Clive Owen never does anything physically superhuman. I don't think he does anything I couldn't do myself. For much of the time he's wearing flip-flops for heaven's sake (interesting use of the bare foot like in Die Hard). The way guns are used is different from most action films.
This is one of those films that properly belongs in the 21st century, made by intelligent people reflecting on the world we live in. I came out and I saw a poster for the Adam Sandler film 'Click' which said 'What If You Had A Universal Remote... That Controlled Your Universe?' and I thought, what the hell are you talking about? Why is anyone making stupid films like that?