It's all a matter of perspective, isn't it?
Mary Poppins is the first memory I have of going to the movie version of a book I'd read. I was disappointed that some of my favorite details were missing. As I recall (it's been a long time), it has something to do with the talking parrot on her umbrella.
I've since learned to appreciate the different strengths of book and movie versions of the same story. But, a true reader, I almost always prefer the book.
(I found this link on A Fuse #8 Production.)