Thanks to Netflix instant, I could see the original Swedish film before the American remake screws things up.
I have not read the book (my wife has) but I've heard a lot of good things about it. Even with a 2 1/2 hour movie, it's pretty clear that there is a lot left out in the film. For the most part, it flows well, but it's also clear that the many members of the family are not very well fleshed out in the film and that there are things missing. However there is only one ellipse near the end of the film that is disturbing, but I can overlook that in the long run. It's hard to say much more without blowing any surprises.
The cast is excellent, and the characters are complex and clearly there is more to come in the sequels. I would recommend the film for fans of the genre.