Another place I'm in the minority on; I feel it REALLY depends on the book if we're going to pull out the ol' "different mediums" card. If a book is very concerned with a character's inner life and what they're thinking ("Catcher In The Rye", for example), or if the novel is just very thick with ideas, subplots, etc. ("The English Patient"), I have no problem with alterations or pruning done in good faith.
I don't even have an objection to an "adaptation" that's nothing to do with the book, as long as its good. I'll note it has nothing to do with the book and move on, not a problem. It's when it's a bad movie that it gets under my skin.
This is what happens when you don't get dates in high school.
To be fair (and reading my post I see that I wasn't, entirely), Fincher is far from alone concerning this problem, and directors are rarely consistent. Stanley Kubrick was pretty faithful to "A Clockwork Orange", but not other books he adapted. Anthony Minghella actually made "The English Patient" intelligible onscreen (no small feat), and then inflicted something he had the nerve to call "The Talented Mr. Ripley" on us.
Oh, and I have no trouble with shocking imagery; it's just there has to be more underneath it. David Lynch, David Cronenberg, and Mr. Penis Drill himself Shinya Tsukamoto all have made films that can be disconcerting in their displays of gore, sex and combinations of the two, but they have always used it in service to a larger message or to advancing the characters. Used otherwise, well...you're left saying "So what?"