It's not long since I finished reading the book - and now the movie. The Swedish version, that is. I saw somewhere that there is an American film at the planning stage, but I can't imagine how an American version would work.
We went to see it at the IFI (great spot for free WiFi by the way), and I was expecting a full house, but far from it - there were plenty of empty seats. I enjoyed it - like the book, it's a long movie (152 minutes). It's quite faithful to the book. All the main turning points are exact replicas, including some quite horrifically graphic scenes.
Some elements are not explored in any detail in the movie, like Blomkvist's relationship with Erika Berger and with Cecilia Vanger (that would have added another hour to the movie without progressing the action in any meaningful way, so I think it was a good decision). Some things have been changed completely - in the book, Blomkvist's investigation into Harriet Vanger's disappearance is kept secret to the rest of the family - the official story is that he is writing a family history; in the movie, on the other hand, it's all in the open, and there is even a family meeting where his investigation is discussed by all. Also the circumstances of Martin's death are very different. And there is a crucial scene added at the end, which explains a lot about Lisbeth Salander (the girl with the dragon tattoo) and her outlook on life. Not a hint of that in the book. And I'm 3/4 of the way into the 2nd book and that past history still hasn't been uncovered at all. In a way, that's a spoiler in the movie. They should warn people not to watch that scene if they haven't finished reading the trilogy!
The actress who plays Lisbeth Salander is spot on, and Mikael Blomkvist (Michael Nyqvist) is excellent too (if a bit older looking than I had expected - he looks very familiar, but I've never seeen any of the movies he's been in). I found that Erika Berger was a lot older-looking than I had imagined, and not as attractive really.
A bit of trivia: Noomi Rapace, who plays Lisbeth Salander, apparently got her nose and her eyebrow pierced for the movie, but the huge tattoo she sports on her back is not real (that would have been an extreme way to get into the role!).