The movie actually has three longer tracking shots. The first one is in the beginning, and if you don't think about cinematography in movies while watching them, you could easily miss it - which is fine. The cinematographer for the film has said more or less the point of the longer shots isn't to "show off" but rather to involve you in a scene in a deeper way. Having a seemingly uninterrupted shot draws you deeper in. The second long shot is during the car ride in the middle of the film, and is, in my opinion, terrifyingly effective. Then of course there's the urban battle at the end which is pretty awesome.
Chldren of men is already being studied in film schools and will have a legacy way larger than its original commercial life.
Incidentally, one of my favorite things about this film is that there is so little exposition - there are a few lines of dialogue here and there, but so much of what you need to know about the world in which this story is set is to be found in the background, on TV commercials in somebody's apartment, a newspaper clipping on a wall, city scenery during a car ride. In a science fiction movie exposition is pretty much the hardest thing a screenwriter has to do deal with - there's too much to explain! - so the fact that they so seamlessly weave it into the story and setting is truly impressive.
If you haven't guessed by now, I really like this movie.
