Books

Dreamcatcher, the movie inspired by a Stephen King novel of the same name.

Anything Resident Evil by Paul WS Anderson. With that, it's like the game franchise is cursed to never have a good live action adaptation.

The Bourne trilogy. I like the books a lot but the films left me a bit meh. Different setting, different characters, different everything.

The 1996 version of Emma with Gwyneth Paltrow as Emma. I don't know what it was about the movie, but it completely put me off Jane Austen as a child and if my sister were to watch any other Austen movie, I wouldn't stick around to watch it. It wasn't until The Jane Austen Book Club was a movie, and I watched that, found out that it was based on a book, read the book, that I would give Jane Austen a go. I decided to start with Emma before the 2020 version came out and enjoyed both the book and 2020 version. I also felt vindicated over the fact that I knew as a child that there was no way that Emma would be engaging in archery as a past time and the book confirmed it for me. Still no idea why the archery was included in the movie.

Eragon. Sooo much changed, cut etc, removed so much depth and story

Masters of the Universe, not that the source material was any good (in my defense I was a toddler when I liked it) but the movie is batshit insane in a totally different way and may as well have been it's own thing.

The Golden Compass. I love His Dark Materials and remember feeling such rage watching the film and how they'd ruined it so unnecessarily.

I love the 1995 Scarlet Letter movie, but it's not remotely similar to the book.

No one will ever convince me there is a worse adaptation than Darren Shan’s cirque du freak vampire assistant. Loved reading the books as a kid. Could not believe the monstrosity that came out.

Eragon.

The movie is NOTHING compared to the book.

Realistically, Forrest Gump was a great movie and a terrible adaptation.

The book was cartoonish and damn-near unreadable.

I love z for zachariah! I saw the trailer for the movie and decided not to watch it. Wasn't that film about a love triangle or something?

Ready Player One was the worst film adaptation. One of my favourite books and I literally stopped watching the film halfway through. I have never done that before, but I was genuinely that angry over how much they changed.

The Neverending Story. Whoever thought it would be a good idea to take a dragon and turn it into a flying puppy should be banned from filmmaking for life. Not to mention all the other ways that this abomination twisted a great book into a complete mess.

I HATE THE Z FOR ZACHARIAH FILM. I'm still mad about it 8 years later and I'm happy to see someone else is as mad as I am. They also made the movie racist so that's fucking wild.

I’m Thinking of Ending Things. Wtf happened in the last like 30mins of the movie!?

Wheel of time. The series is only the same in names of characters and title. They have butchered the story completely. The changes they have made early on have ruined important parts of the series that haven't been filmed yet. I watched S1 hoping it would come back to the books, but I've lost hope and won't watch any more.

Ella Enchanted was one of my favorite books as a child and the movie, while cute, was completely different in plot, tone, and depth. The book was a lot more poignant and serious. Ella had a lot of rage, fear, and loneliness as a result of her life and the 'gift.' The novel doesn't have a true villain except the petty/cruel stepmother and the curse itself. Ella is funny and charming and has a gift for vocal impressions and disguises.

The movie was basically live action Shrek but make it Cinderella and Hamlet. For some reason they thought it needed an evil uncle arc for the prince? And Anne Hathaway is good but the way the film was written, Ella was just a somewhat rude girl boss type. In the books she gets out of trouble often through her personal charm, manipulation, or persuasion. In the movie she does karate and lectures people.

Planet of the Apes. In the novel, the planet is NOT Earth!!!

I watched 2 film adaptations of Fahrenheit 451, both were atrocious

Artemis Fowl

Main character is supposed to be this highly intelligent, no all that athletic, sociopath and the first shot of Artemis in the movie him surfing, riding some sort of mono board and being all sporty. That's just the start, but I knew it wasn't going to be good from that point.

World War Z. An amazing and human retelling of the zombie apocalypse turned into a shitty action movie like all the others.

Tales from Earthsea is this for me. It's more competent than some of the other entries in here, bc it's a Studio Ghibli film.

That said, it manages to miss what makes the Earthsea books interesting, and trades its moral complexity for something way more direct.

I Am Legend. The book is dark, brooding, heavy, and psychological. The movie really Hollywood'd it up, completely changing the entire point of the ending.

Dark Tower

V for Vendetta

I felt like the movie focused too much on action, and not enough on the dark, psychological themes of the graphic novel (which was more of like an atmospheric/gothic dystopian tale). The movie felt like a clear cut "good guy vs. bad guys" situation, while the novel was a little more nuanced in its approach to its characters, morals and dilemmas.

The Movie City of Joy took a minor character from the novel so it could be a vehicle for a Hollywood star, in this case Patrick Swayze. I think World War Z, mentioned elsewhere on this thread, was guilty of the same, but I can't remember if Brad Pitt's character is even in the novel.

Stephen King’s The Dark Tower series was adapted into such a god awful movie a few years ago that most King fans pretend like it never happened.

We are all holding out hope that Mike Flanagan will save us.

Artemis Fowl

The Maze Runner series, specifically The Scorch Trials. The first movie changed a lot (the WCKD instead of WICKED really irked me) but the second movie completely deviated from the plot of the second book, it was unrecognizable.

Watership Down - the Netflix/BBC adaptation. Significant changes to plot that invalidate half the story, and animation from 90s PlayStation games.