This questions applies to any film based on a book.
For me, I would have a hard time reading the book, because I know from seeing the movie, what will happen. At the same time, the book will offer much more detail, character development and background than the movie.
Thus, I strive to read the book first when I hear of a movie coming out that I think I´ll like. Anyone else feel that way?
I agree.
Also, we all have our own imagination where films may not be able to compete in that capacity.
There are many reasons the film may deviate or make changes from the book.
I say if the book is good, ok.
If the film was good but...ok to that too.
I read Mario Puzo's novel The Godfather after seeing the film. And I still enjoyed it although there were some differences in the movie.
And....... Great film, great book.
Besides, we can't point the blame on the movie people, entirely, if it differs to the book.
Sometimes the author and movie people cannot come to an agreement towards a certain scene. The result is to cut it out and move on.
The sad fact is I usually see the movie before reading the book. Lazy, I guess.
I do not think that has diminished my appreciation for the novel. Nevil Shute's "On the Beach" and "No Highway in the Sky" being two examples. If anything, the movie helps illustrate my thinking about the novel. When there are wide departures or let us just say, "creative interpretation" by the movie makers, I take it in stride and accept it for what it was. "The Big Sleep" being an example and "The Long Goodbye" being another. Although, I have to wonder what Robert Altman was drinking back in the mid 1970s.