I’ve written before about my opinion of several then-recent movies adapted from favorite novels. Though some were better than others, I felt that each movie—even those I pronounced “great”—was not nearly as good as it could easily have been, because the books were far better and the movies had made so many unnecessary changes (several of which were simply bad decisions even ignoring the books entirely).
But then there are the few gems that are both quite faithful adaptations and brilliant productions per se. The ones I’ve seen, where I knew and loved both books and adaptations, were the first two in the Harry Potter series and the BBC Pride and Prejudice adaptations. What made these succeed when others failed?
I think each one’s success came largely from a different facet of the same reason: each took the time and effort necessary to fully portray the essentials of the book. In the case of Pride and Prejudice, this meant five or six hour-long episodes, and in the 1995 version the addition of a few scenes shedding light on the characters. Some truly extraneous action may have been cut from the book; I don’t entirely recall. The other two visual adaptations, into feature films, had to condense the plot considerably, and the story suffered significantly. (I intend to write a comparative review of the four adaptations on this blog … sometime, eventually.)
By contrast, the Harry Potter films (I restrict myself to the first two—I’ve only seen the first three, Prisoner of Azkaban in my opinion isn’t a very good adaptation primarily because it broke visual continuity with the first two so severely, and in any case I like the books after the fourth less and less) work well as both adaptations and films because so much of Rowling’s text is either description that translated well into comparatively brief “visual storytelling” or entirely extraneous: in other words, because there is simply so much to cut without harming the story in the slightest. (Note that I think Rowling’s true and lasting literary success should be measured more by the sheer number of better writers she drives to write fan-fiction fixing the problems with her books or otherwise set in her world than by the seven books themselves.)
In general, it is a rare novel (that is itself any good, anyway) that can be faithfully translated into a ninety-minute film that is both a good film and a good adaptation. A film is the visual equivalent of a short story, or at most a novelette or short novella. Examples of short stories that have been successfully adapted into movies abound; I’m told that Blade Runner (based on the story “Do Androids Dream of Electric Sheep?”—I’ve neither read the story nor seen the film) was one, as was <Minority Report (which I have seen, but I haven't read the story it was based on). The visual equivalent of the novel is the mini-series; you simply need several hours to do a 80,000-100,000-word story justice.