My biggest pet peeve is when someone tells me that I didn't like a movie because I read the book. I've been reading books my whole life, I've always wanted to be a novelist. But I studied film in college, live and work in Los Angeles, and I fell in love with screenwriting. I think I have the mental capacity and background to form well educated opinions about books and movies and adaptations.
This is what I look for in an adaptation:
-It's a good movie. I need it to be well written as a movie first. That means the movie structure is there and the story and characters are understandable whether or not you've read the book.
|Orlando Bloom is entertaining to look at.|
-It's entertaining. Movies that aren't entertaining very rarely keep an audience and what is entertaining in a book is not necessarily entertaining on screen. The filmmakers can't be afraid to make changes that will make the story a better movie.
-It keeps the spirit of the books. A book and a movie are totally different formats. Imagining shooting a movie straight out of a book should make you laugh. Very hard. But if the filmmakers change too much, they isolate their built-in audience. Which is bad (The Twilight franchise knows it doesn't need to be any good to make bank at the box office). But keeping the spirit of a world or story will usually keep fans of the book happy and will probably help preserve whatever it was that made someone think the book would make a good movie in the first place.
Lord of the Rings was a great book, but it was also a great movie. It was easy to follow (which is helpful even for those of us who have read the books, because... hello, complicated!), beautiful to watch, and highly entertaining. But it kept the essence of the books; it really captured Middle Earth.
A very different example is A Series of Unfortunate Events. The books and the movie were so different but I loved them both. The movie changed a ton, because they combined the first three books. There just wasn't enough in one (very entertaining) book to make one (very entertaining) movie. But they kept the spirit of the books--that dark, dark comedy--and it made the movie work for me.
I usually only post about movies when things don't work, and even then I only post about it rarely. Check out my posts on casting Jennifer Lawrence in the Hunger Games, My letter to Chris Columbus after I watched Percy Jackson, and Why Part of me hated Harry Potter 7 (I know, I couldn't believe it either).