An excellent film, but maybe it's not for everyone, especially if you think that movies like M. Night's Unbreakable move 'too slowly'. The Son is more along the lines of a character study. It takes a while to start to really go somewhere, but really gets you hooked once you start to get some information on some major details about the characters' and start forming ideas of where the film is headed. This is one of those films that should be seen without reading anything about it ahead of time. I'd say it's a must-see for anyone who truly loves film.
This is one of the best films of 2008, the best film I've seen so far from Kore-eda, and a worthy addition to the Criterion Collection. This story of a man bringing his new wife and her son from a previous marriage to an uncomfortable visit to his parents' house to observe the anniversary of his older brother's death is approached with a different tone than your typical movie, more realistic and truthful and at times more subtle and meditative. We are witness to this family's disappointments and the petty grudges that sometimes separate loved ones, while people pretend to put a happy face on things at the same time they are sneaking in passive-aggressive comments. There's a bittersweet beauty to the film. If you like a film like this, you might also enjoy Yojiro Takita's "Departures", another excellent Japanese film from 2008 (my favorite film of that year and the Best Foreign Film Oscar winner).
I also liked how the Criterion dvd's menus used the poetic, Ozu-esque 'pillow shots' from the film as opposed to a big movie studio's dvd menus, which often risk spoilers to be flashy.