I finally caught the movie. I thought it was excellent.
I'll be that guy and say the book was better, but that's not surprising given it came first. The film missed a lot of interesting stuff from the book (the history and significance of the 'Amazing Amy' books; Amy's relationship with her rather dysfunctional parents; Desi's family history and his relationship with Amy; the depressed U.S. economy generally, and the town's depression in particular; the Dunnes' own financial struggles). Of course, the film can only do so much, and I think the appropriate material was edited out for the movie.
Re: casting, I thought they nailed it (for the most part). Affleck was perfectly cast in the role of Nick (though I thought his performance wasn't the best). Pike was dead-on as Amy. The detectives and Margo were also well-casted and acted. Emily Ratajkowski as Andie (or, well, in anything really...
) NPH didn't match up with what I thought, but he did a good job.
As an aside, I can't believe how many scenes in the film looked exactly like I pictured them when reading. Maybe that's because the novelist wrote the screenplay, but so much of the film looked like exactly like I imagined it - the Dunne home, the bar, the police station. For me it was almost surreal. And yes, i know this doesn't make it a good movie.
I guess I'm one of the few who loved the ending. It seemed to me the only plausible closure. Amy was smarter than Nick and he knew it. Any other ending would have felt forced imo. It also put a significant exclamation point on the story's twisted view of intimacy and relationships.
As for Fincher, this is one of his better films imo. My favourite will always be 'The Game', but this is in his top three for me.