A pretty decent movie, more to be watched for its setting and its cinematography than for its plot or its characters.
Children of Men portrays a dystopian vision of a world in which women stopped given birth, people lost hope for the future, civil unrest arose, countries became xenophobic and closed their borders, terrorists and police states appeared, and, in short, everything's gone to hell. Yet, the world Children of Men reveals, with no new capital investments or technologies, feels close enough to the modern world--simply aged and run-down--that it hits home as (uncomfortably?) plausible.
The movie conveys this world through great attention to detail. For instance, old newspaper headlines appear throughout the film, especially in one shot of a room where the walls are covered with them. IMDB collected a list of these headlines (scroll down). Although I couldn't read most of these headlines while watching the film, I cite this as an example of the movie's meticulous nature.
Indeed, the Washington Post reported that the director, Alfonso Cuaron, said,
"Chivo [the cinematographer] used to say all the time, 'We cannot afford one single frame without a comment on the state of things.' The story of this movie is just the coat hanger. What's important is the fabric that you're going to hang."
However, while I found the setting--the fabric--interesting, I'm surprised they didn't seem to hang a message on it. Although the film strongly involves repression of immigrants, it doesn't make much of a statement about it.
The quote is also unintentionally revealing about what they didn't pay attention to. I thought the plot lacked cohesion. I also thought the acting was pretty poor. Only the main character was decent, and that's because he's a man of few words.
In addition to deserving commendation for its setting, the movie the movie also exhibits some extraordinary cinematography. For instance, near the end of the movie is an impressive seven minute long continuous shot action scene, encompassing a tunnel, two city blocks, and multiple levels inside a building. It includes gunfights, major explosions, deaths, and many extras. It's amazing they got it to work fairly well. The blood on the lens is a nice touch, likely unplanned. (How many takes would they film in an attempt to get the scene?) There are other technically sophisticated, difficult, and long takes elsewhere in the movie as well; I focus on this one merely because it stood out more for me.
Although it's definitely an action movie, there wasn't as much action as I expected. In retrospect, I realize there was a lot of action, as the scenes cited above support, but it's just that the action isn't flashy. The hero is reluctant. He has no amazing abilities. All the action and the world feel of desperation, nothing like action in, say, the style of James Bond.
Incidentally, I learned from reading reviews two features I never consciously noticed while watching the film: one, the hero never carries a gun; two, there are no close-ups.
Spoiler: it'd be interesting in a number of ways if the movie ended as Kee sat waiting for the boat.