I'm going to keep this brief.
It's been a while since I've read a mystery. Probably not this long, but the last one that comes to mind is And Then There Were None, by Agatha Christie, in 8th grade. I remember liking it. Maybe I should reread it...
Here's what I thought was so clever about The Girl With the Dragon Tattoo. (Warning: this will not be anywhere close to insightful.) It was entertaining, although not a markedly quick read for me, all the way through. Of this 590-page novel, the first 440 were enjoyable, but not especially heart-pounding.
But the last 150 pages flew. With about 140 pages left, I was not going to put the book down, (partially because I was so curious what else Larsson could do with the story in that many more pages) because the plot just kept taking another turn--while at the same time coming more clear.
It was really well executed, and a fun read. Don't expect it to be quick and easy, but do expect it to be worth the time.
Found out via twitter today that the Swedish film adaptation of The Girl With the Dragon Tattoo will be coming to theaters in the United States on March 19. Bookpage has a description and trailer here.
Also, I understand there is going to be an American film adaptation as well. It could be, though, that I misunderstand that there is going to be an American film adaptation as well, so I will have to research the matter and update this later.