There isn't much more that I can add to the previous comments. The film is wonderful, had only one flaw (imo the sometimes too "sweet" music), and it's situated in this space between documentary and fiction, which is the thing I love most in films. The direction is marvellous, as the film gets better and better, and is one of those rare examples, where the director lets the film find its own pace.
There are some outstanding scenes in the film, that can be compared to ANYTHING that has ever been put on the screen, that oscillate between the screen and the viewer, creating a sort of third reality besides film and the real world. My favorite scene is at the end of the film, where 
*spoiler* 
the t kids and their friend are sitting in a train after having buried the youngest, and the camera just pans them.
*endspoiler*
This is exactly why I watch movies, when it becomes clear to me that I don't know any other artform which can express feelings as sublimely as film. In such moments art transcends life, creating situations that in normal life would maybe called "miracles", and Koreeda lets us because he never judges his characters see human beings as they are. The film thus becomes a perfect example of humanist filmmaking.
One of the best films of this year, which will probably end up in my top ten of 2005.