Many times when reading a book I will visual every scene in my head. Often when the book is turned into a film adaptation I only notice the differences between the two.
A lot of popular books include details that don’t translate well to screen. This is for a variety of reasons and personally I think the biggest one is that some effects just don’t look realistic. In “Twilight” it came across as awkward when certain details didn’t work on screen the way we pictured them in our heads. The sparkling and the werewolf transformation being the biggest two for me. There were differences in how the characters acted as well. If you want to read more differences between the “Twilight” novel and movie check out this article on the Examiner.
Often fans of movie versions of books will like both separately. I have liked books and the film adaptations as different stories, but when comparing them only noticed the differences. It’s easier to enjoy a film adaptation when you haven’t previously read the book. It keeps you from having preconceived notions of exactly how the movie should be and the disappointment when your favorite scene doesn’t make it onscreen. Here’s a poll on Goodreads showing that most people prefer reading the book before seeing the movie.
Personally I find it fun to go see movies based on my favorite books. The same goes for watching TV shows based on books. However, I have to remember that not everything translates well between the two mediums. When one of your favorite scenes or characters gets cut from the onscreen version, just remember you can go back and reread the book.