First things first: In a lot of ways, the movie sets it up to be better and more interesting narrative. Instead of being told by the author (as you are in the book) what's he's doing, you have a grandfather telling the young boy the story. The connection between the person 'reading' the story to someone else (grandfather to sick grandson versus 'abridging author' to novel reader) makes a lot of it more compelling and interesting.

Second: I know when it was written, but the constant jokes on fatphobia and the misogynist marriage are frustrating. It's kind of 'tongue-in-cheek', but it's also really quite infuriating to keep seeing something where Goldman's 'wife' is thrown under a bus for every minor thing. I wasn't expecting that, and it's probably what made the movie feel much better (even if Westley and Buttercup's relationship, in any form, isn't the healthiest).