Due in part to the recent(ish) chatter about how faithful an adaptation The Watchmen is or is not, I've been thinking about book-to-movie adaptations. Personally, like most avid readers, I think, I'm a purist. I want the movie to be the book, just on screen. I'm upset at anything being cut, I'm upset if the actors don't have the right look, I'm upset if the general feel isn't the same...
But isn't it almost impossible to be entirely faithful even if that's the goal? Simply put, there is no way to make a movie that is the book in all its important aspects. The media are too different, our way of interacting with them is different, and it just doesn't work. Most obviously, any length book, from Where the Wild Things Are (trailer!) to Les Miserables, have to fit into basically the same length of movie time, so something almost always has to get cut, or occasionally things have to be expanded.
Then also, books are often advanced through characters' thoughts or descriptions, and these may not translate to film very well. Nobody wants to watch an A Clockwork Orange that is virtually indecipherable because of all the slang (and that takes place in an almost-constant voiceover). Descriptions of scenery or people pretty much have to be conveyed by simply showing them, which isn't quite the same (depending on the author's style, I guess). It's quite difficult to convey the same sort of feeling visually that is conveyed through words, especially as the words definitely don't convey the same sorts of things to different people, and the images may not either. So as a movie maker, you're stuck making decisions about whether to transfer a given set of words into voiceover or rework them into dialogue or whether to convey the same idea visually or set the stage with background music.
Some of the worst book-to-film adaptations I've seen are the word-for-word entirely faithful ones (e.g., anything ever viewed in an English class—Julius Caesar is my personal example of this). Boring! Maybe the problem there is that most canonical books don't ever get to be big-budget movies; they're always stuck being made by literary purists on shoestring budgets. They're not at all artistic. And really, artistry is necessary to make a good adaptation. But this is where you get into trouble with the purists. "They cut out [minor character]!" Yes, because they take up too much time / aren't essential to the plot / whatever. "That's in the wrong order!" Sometimes flashbacks or otherwise chopped-up timelines that work in books are disorienting in movies.
Personally, one of the issues I have in watching movies based on books is that the way I visualized settings or characters isn't ever the way the people who make the movie visualized them, and probably isn't the way the author or any other reader visualizes them. That's kind of the point with books, right, is that you get to visualize it however you want? I can usually get over this, except when it's a book who has main characters who are (a) small children, or (b) animals. In these cases, I think one must be very careful not to take the movie making too seriously and be too faithful. Talking animals that may be perfectly reasonable in a book (largely because you—or at least I—do not fully envision them as real, live animals but rather some slightly fuzzier and less realistic representation of one) look pretty ridiculous in a movie. (e.g., Aslan and the beavers and such from The Chronicles of Narnia) When I first found out they were making a movie of Ender's Game, I was quite concerned, because although when you read it, you know he's only six years old or whatever, it's not quite the same as staring at a tiny six-year-old actor being a freaking genius, or worse, trying and failing. (I guess I won't have to worry about that, though, because they ended up canceling the movie idea.) I guess I can only suspend belief in certain areas—in a book, a talking lion is no biggie, but when there is a lion on the screen, moving his mouth and looking all serious, I find it a bit ridiculous. I would prefer animated versions of these sorts of movies, probably, to relieve my discomfort over this sort of thing.
I think the problem with movies based on books is that fans of the book, other moviegoers, and movie makers all have different expectations from the process. Readers want what I described above (mostly), but can sometimes handle a few well-justified cuts or changes. Everyone who sees the movie without having read the book either wants to know what the story is about or just wants to enjoy a movie. ("Oh, there's a book this is based on. Cool.") The movie makers, however, want to create something. Yes, they took the idea from a book, but their goal is almost never to recreate the book. They want to create something new, a parallel version of this story, or even a much-adapted version emphasizing the parts they think are most significant (or introducing things they think would make it better). I'm sure there isn't much artistic satisfaction in simply translating the written word to the screen; they want to make something new and yes, probably different, to reinterpret something interesting through another medium, to look at it from another angle. I'm trying to realize this and have a more open mind for adapted movies.
Of course, sometimes the adaptations/reinterpretations are so radically different that you wonder why they even bothered keeping the title the same. For instance, 2001: A Space Odyssey is apparently a brilliant and groundbreaking movie on its own terms, but as far as its relation to the book? Not so much. I can't decide whether Kubrick expected people to have read the book or not. I can't imagine that anyone unfamiliar with the book has any idea what's going on in the last half of the movie, especially the Star Child bit. Maybe he likes it that way?
I realized at some point in college that I was approaching the impending release of movies of books I liked all wrong. I'd hear a movie of whatever was coming out, so I'd go reread the book to refresh myself. I would then see the movie and, the book being fresh in my mind, would be indignant about whatever (often relatively minor) changes they'd made. On a couple occasions, I intentionally waited until after seeing a movie based on a book I had not yet read to read the book. I don't find this a good strategy either, because then I visualize the characters the way they were in the movie, and I end up pretty conflicted about which version was better because the movie had compromised my starting point. (Since I generally enjoy books more than movies and think of them as the default and the right or original version, I don't want my experience with them to be contaminated by having seen the movie.)
I finally realized the secret is not to know the book like the back of your hand, and then you'll be happier. Having read the book about six months to a year prior to seeing the movie is pretty much ideal. You are familiar enough to enjoy it all and to have the big things straight, but if something minor is changed, you don't flip out about it. It's nice and drama-free. (Your ideal time may vary—I pretty much have a horrible memory for books and movies, so my detailed memory of them degrades pretty quickly. If you're the sort of person who can recite lines from movies you only saw once and that years ago, you probably ought to have a wider window of time.) I think I read The Watchmen around September or so, then saw the movie in March. That worked, but only because I'd never read it before. For a book I've read more than once, a longer period of time would probably be required.
Tangentially related, I hate, hate, hate it when books put out a new edition, the cover of which has the actors from the movie on it. Viggo Mortensen, though I'm sure he makes a very nice-looking book cover, is not the only Aragorn in the world. I find it again limits your visualization process but also seems to give the movie more power over the book than I'd like. The book is the book, and if people really need to see the actors to remember what movie it was to be tempted to buy it, that's sad. Really, Barnes and Noble can put them on the "the book is always better" table, and people will pretty quickly realize, "Oh, this The Reader is what that movie The Reader was based on!"—no Kate Winslet required.