Last Saturday, D and I saw Children of Men (after it finally opened at our local AMC), and it is amazing. One of the best of last year, no question.
You can compare the premise to any number of dystopian future visions--D picked Damn Nation; I went for Y: The Last Man--but Children of Men breathes life into its ideas, making the fantastic plausible but never mundane. Yes, there is at least one MacGuffin. Yes, the movie could have been a lot longer and more sprawling. But this film knows what it is and isn't about, and sticks to its story, and I think it's stronger for that commitment to narrative.
I also need to mention the phenomenal cinematography, which features several long, continuous tracking shots, simulating the gritty reality of a documentary and giving the action scenes a visceral immediacy. I'd argue that Children of Men is worth seeing for the Bexhill sequence alone--yes, it's that fucking good. You may not like everything this movie presents, but it will affect you.