It’s a fight that has been waged since film became a viable storytelling medium.
The book or the movie the book spawned (sometimes the opposite!) has been a war that has been waging for years.
A few weeks ago, I read the Russian book Night Watch. I told someone about it and found the films Night Watch and Day Watch (both are based on stories in the Night Watch novel).
We watched the films and over the course of several hours the differences between book and movie were enormous. At the end, my friend asked “You liked that book??” the tone of his voice made it clear that he disliked the film, just as I had.
I then tried to counter by telling him exactly what was different, that you can’t judge a book just by watching the movie based on it. In all, the film contained about 30% of the story from the novel and changed around a lot. Some of it good, others bad, mostly bad.
I did like a few of the scenes of the Dark vampire family, trying to live like normal people despite being outcasts in the human world and in the Other world.
I don’t want to say it was an unmitigated mess, but it’s one of the things where the film is the film and the book is the book. There is no comparison.
That said, I loved the book. I plan on getting the rest of the books in the series. It’s almost a “What if Harry Potter became an IT administrator and part-time Auror in Russia.”