I'm re-reading the Lord of the Rings trilogy for the first time since having watched it movie form. While I remain pleased and amazed with the beauty and caliber of the films, there's a palpable difference in detail between the two media. This missing detail is both a bane and a saving grace for the movies, in my opinion.
The "bane" role is easy to understand. Parts of the story are lost when one watches the movie—parts that Tolkein as an author ostensibly thought necessary to make the story whole. Had he thought them extraneous or worthy of omission, these parts would have been included as extra (dare I say... apocryphal?) stories in tomes similar to the Silmarillion. Because of these missing details, thousands of people know an incomplete version of the Lord of the Rings. These people are either convinced in the movie's detail-completeness, are too lazy to read actual books, or both. The missing details are glorious and, in this reader's opinion, make the books far grander and loftier than the movies.
Despite this obvious shortcoming, the omissions made in the movies are palatable. One could even argue that they allow a book lover to watch the movies with what I will term recoverable loss.
Of what "loss" do I speak? It is soon told. A reader's imagination is a fleeting thing. Give form, mass, scent—any quality, really—to the scenes or characters in a book, and the imagination seizes on those qualities like an engine poisoned with sugar. What should be wild and inchoate becoms stagnate, stillborn. Despite its best efforts, the imagination can not budge: it must attribute those qualities to that scene or character. Who can but picture Sir Ian McKellen when hearing the name "Gandalf"? McKellen himself is two years younger than The Hobbit, the book in which Gandalf made his first appearance as a fully-grown (and fully-aged) wizard. By the time McKellen had grown up, trained as an actor, and been cast as the Grey Wizard, Gandalf had already lived his unadulterated role for years on end. Therefore (and quite naturally), McKellen must act to fit this role, not to define it. It also follows that McKellen can never be more like Gandalf than Gandalf himself. But by watching McKellen play Gandalf—unless one is careful to the point of detachment—the movie goer sees him redefine and encompass a role that should be defining and encompassing him. Regardless of how well or poorly he acts, his face is now irrevocably superimposed on Gandalf's. The reader's imagination and Gandalf's character have been subverted; only time and sheer force of will can erode the figure of Ian McKellen and replace it with something personal, something interpreted by the reader rather than told to the reader as interpreted by another.
This is the loss of which I speak, but I term it as recoverable for a reason. The minutiae that are missing in the films provide escape for the reader's captive imagination. They set it free by requiring it to operate on characters, scenes, and situations not defined by the movies. They are cracks in a fortress, making imaginary revolution real (whew—that's a tongue-twisted play on words). A dedicated reader can watch, enjoy, and work to forget the movie's interpretation. While the amalgamated imaginings of Peter Jackson (and the other minds that helped the movies come into being) are artistic, well-compiled, and can be correctly described by many other positive adjectives, they are incomplete.
There's often debate about the interplay between the meaning (or lack thereof) an artist intends for a piece of art and the interpretation an audience member gives to that art. I'm not going to touch on that debate except to use it as a referential compass for evaluating movie watching. When a film maker renders a book on film, a second layer of interpretation is added. The film maker becomes an artistic middle-man, both obscuring the artist's original meaning and influencing the audience's interpretation. He or she acts as a preprocessor to the story, omitting or embellishing with impunity. Audience members that watch the movie without reading the book have, at most, their own interpretations of an interpretation.
Ah, interpretation. Movie versions of books can be useful, for two reasons. In one sense, it's a modern form of oral tradition—applied once. There's some staying power in a story that is reinterpreted and told again. What I find more interesting, however, is the ability to evaluate another person's interpretation of the original work. As if part of some literary form of triangulation, obtaining an additional data point helps me in my own interpretation. Accepting, rejecting, or ignoring another person's opinion about what a story says helps me refine my own opinion, and hopefully see a fuller picture. But that other opinion alone could never suffice.