Book to movie adaptations always make me really nervous. For some reason the movie versions never seem to live up to the story told in the book. I know it's not fair to expect a movie to capture every detail, back story and especially vivid subtext evoked in a book. I always try not to get my hopes up but it never works. I am at least disappointed, at worst appalled by what filmmakers have done to the stories I read.
This is especially true with books that I love. The ones that I reread until the spine has cracked in half and chunks of pages are falling out. And nothing gets my goat more than when I walk into a bookstore and the powers that be have replaced the original cover with a screenshot from the movie and splashed "Now a major motion picture!" over the front in an obnoxious font that is usually bigger than the author's name. Come on now.
The best is example of this, for me, is "The Notebook." The novel is written by Nicholas Sparks and - although I don't generally read Sparks' books because they tend to be a little sappy and lacking in dragons - when the movie came out I decided to read the book first. You know what? It was pretty good. I liked the main characters - especially the woman who was pretty feisty - and thought it would probably make a good movie.
Then I went and saw it. I hated it. By the end, when the theater was filled to the brim with crying women, I was choking back laughter. I actually like the movie now, having re-watched it without the book as fresh in mind, but I can still see where they made the most offensive mistake Hollywood can make when turning a book into a film.
That unforgivable offense is changing details unnecessarily. This, along with Emma Watson's constantly wiggling eyebrows, is the main reason I cannot stand the Harry Potter movies. I understand that to fit an entire novel into a neat, two-hour package some details will have to be changed or cut out completely. That's fine. But killing off the main characters at the end of the movie for no apparent reason rankles me. In the "Harry Potter" saga the movie makers inexplicably changed the final epic battle scene. If you haven't read it, skip the next paragraph because it contains some pretty big spoilers.
In the book, Harry rises from the (apparent) dead and returns to challenge Voldemort in the midst of a massive battle. The fighting around them stops as everyone turns to watch the duel. When Harry wins, Voldemort dies and his followers drop their wands, surrendering to the good side.
In the movie, Harry and Voldemort engage in some sort of weird flying around alone battle. Voldemort still dies - I think that detail would have been too big to change - but nobody else sees it and he sort of disintegrates into the wind.
Why? "Lord of the Rings" proved that epic battle scenes resonate with audiences. The book ending also makes the not so subtle point that Voldemort was human. When he actually died, he was a corpse just like everyone else and he would not be coming back. Having him blow off into the wind might make people who haven't read the books think he could come back, It just doesn't make sense to change something like that.
Occasionally, producers can get it right. To illustrate, I point to the shining example that is HBO's Game of Thrones. I have read the books multiple times and watched the first two seasons of the shows with absolutely no complaints. They do occasionally change details, like having Arya Stark serve as cupbearer to Lord Tywin Lannister instead of Roose Bolton, to get pertinent information to the audience. They also seem to expect that you've read the books - even though social media suggests that most of the audience hasn't - and don't over-explain every detail. That series is great and you should both read it and watch it.
My friend has a conspiracy theory that authors intentionally allow movie adaptations to be bad so that the books look even better by comparison. I almost hope it is intentional because it would make me feel better about the intelligence of Hollywood. As more and more movies are based on books I will be crossing my fingers that the producers take the "GoT" example and stay true to the original story.