Both Neil Gaiman's book Stardust and the movie were good, but there were two changes I hated.

First: >!The unicorn unchained the star. Tristan taking the chain off her, instead of leaving her alone chained up to a tree is a major plot point because that's when he started to see her as a person, instead of an object. It's later called out by another character that she wouldn't have helped him if he hadn't freed her. In the movie, though, he just ties her to a post and leaves her, and then a magic horse comes by and breaks it.!<

Second: the ending >!In the book, the witches realize The Star's heart belongs to another and stealing it wouldn't give them youth anymore. So there's a little chat between them, it's handled delicately, and when offered a position as king Tristan says "sure, when I get around to it" and spends several years heroing while his mother rules in his stead. In the movie, there's a big cinematic battle where Tristan fights the witches with a lightning cannon, rescues the damsel in distress, and then goes straight to being a prince in pretty clothes.!<

They both make for a more marketable movie, sure, but they're also directly in conflict with what made the book so special. As someone who grew up reading Cabell & Mirrlees, it felt like a betrayal of the story.