I'm only 28 and my wife is 30, certainly not different generations, you 25 year old whippersnapper.
I have seen quite a few violent movies and played some violent video games, but that is not where my argument comes from, let me try to rephrase it.
I agree that the sex and violence were actually done well. Nothing was gratuitous or over the top at all. The book certainly is dark and the film captures the psychotic nature of the antagonists well. My problem was that in the limited scope of film, time becomes an issue and it seems to me that the focus of the movie became the sex, much more so than in the book. I think that my wife, not having read the book but having heard me praise it quite a bit, thought that the book must have had violent, murderous sex as a central theme as well. And while it is in a way, I don't think it is as up-front as the movie makes it seem. The pacing and very nature of a book, of course, allows for more internal development than film can portray, limiting a director to what can be shown visually. This conflict will likely never be solved to the satisfaction of those who both read books and view films.
I also think that because of this compression the slow revelation of the mystery was compromised. Because of the large time-frame the book encompasses (almost a year), I understand that it would be difficult to portray this.
As to the omissions, I guess I will explain myself as to the three biggest (in my opinion). So:
******SPOILER WARNING*******
I think that the biggest omission is that Vanger doesn't promise to give the damning information about Wennerstrom to Blomkvist. In the book Blomkvist initially refuses to enter the investigation and is only reluctantly drawn in by the lure of getting back at Wennerstrom. I don't know why they didn't put this in, it is somewhat alluded to in the interview between Frode and Salander, but never returned to. Instead, the information comes entirely from Salander, which most of it does in the book, but not without the first push in the right direction from Vanger. I think that this difference really changed the feel of the final revelation and changes the portrayal of Blomkvist's motivation. He may actually be a more sympathetic character in the film because he joins in only for the reason of finding Harriet (and probably the fat paycheck). In the book he is also motivated by the feeling that he got screwed over in court and Vanger dangles the opportunity to get his revenge, but only if he does his best in trying to solve the disappearance.
The second omission is less important, but becomes important in the second and third books. At the end of the book and the movie Salander steals all of Wennerstrom's money. In the book she steals billions of kronor, in the movie it is downgraded to just a few million. It is this money that frees her to do whatever she wants and purchase her condo and high tech equipment in the second and third books. With the exchange rate of about 7 kronor to 1 U.S. dollar, she wouldn't be able to afford everything that she is going to have to buy in the next two movies. Is this pedantic and trifling? Probably. It could also be a translation problem, I don't speak Swedish, so perhaps the movie was correct and the English subtitles got it wrong in writing "several million".
The third omission is not really an important plot point, but goes to revealing character. In the book Salander visits her mother at the nursing home every week. The movies shows her as never having visited at all until the events of the mystery force her to realize the importance of family. Like I said, not crucial to the plot, but it makes Lisbeth a colder character to know that she has never visited her ailing mother.
I don't think that I have ever written this much about a book/film comparison without it being a school project.
I really enjoyed it though and would like to hear your reactions.
