I say you can never compare a movie to a book... no matter how hard you try it's not the same.
If a movie is made after a book it will hardly ever be just like the book. First because of the different views of the author and the director. And plus, a two hour movie cand never include everything that is in a book that takes one, two days to read. So the movie will be a shrtened, and many times important things are left aside.
And secondly, there are also movies that you can never put in book. There are movies where every screenshot (don't really know the word here

) is like a picture, like an art fotograph... So how do you put that in words?
Cinema and literature are two different arts...
As for the movies HP, I feel a lot has been let outside, and they leave me a feeling of a shallow thing if you know what I mean... And there is many times a big difference from what I had expected and how the movie has turned out.