How do you feel when an adapted film's story deviates from the original material?
I think people need to understand that those are two different pieces of art. A book is basically a screenplay, and the directors can do whatever the heck they want to the story, but they should keep in mind that they will not please everyone. Especially, if there is a huge fan base for the book, in this case, no self-respecting director should pick up that movie if he wants to keep his credibility intact.
To be honest, I was somewhat disappointed with Harry Potter, where they left out parts i left were important altogether. But I also understood that the length of the novel could not be compressed into a watchable movie.Thats why picking up the novel was such a risky endeavor for the producers/directors. And, I feel like they really DID try to keep all the major scenes in, and thats why it seemed so rushed. There wasn't a lot of time to cultivate chemistry between the characters. The novel was less science fiction and more adventure/young adult. The movie was vice versa.
To me, a movie based on a book is just the directors trying to milk the public for the seasonal hysteria around the novel. (eg: Twilight, Harry Potter) Its cheap, its disgusting, and not really a piece of art. Very few novels could make a successful transition to a viewable platform, so its not the director's fault really. They just shouldn't have picked it up in the first place.