Good film with many missing pieces

The movie itself is really well done and the atmosphere is super built. The two main characters were able to convince me.
Did the film seen once before the book and really only caught half. Then have the book as an audio book belongs to (nearly 18 hours) and then I looked at the film again.
Only then I like a lot of important points was deliberately kept very poor and how many details were shown completely different.
My recommendation is to first read the book and then see the movie because otherwise simply does not understand too much at once or overlooks.