I'm so happy that everyone hated Eragon...I really liked the book and then I watched the movie and WTF. Ugh. I'm not sure if the Eragon adaptation is the worst ever or if Inkheart is. They're both abominations though.
Series of Unfortunate Events was bad but at least it looked nice.
Harry Potter and the Prisoner of Azkaban was terrible...I'm REALLY happy to see so many people hated it too, all of my friends like it the MOST. Ugh. Goblet of Fire was bad as well but at least I can rewatch it.
O! and all the teenage crap made from Shakespeare's plays...although O! was definitely the most insulting.
The Legend of the Seeker, which is a tv series I know but it was like someone had read the first half of the back of the first book and decided to make a show from that. God awful. And it's my favourite book series, too.
The Twilight movies are really terrible; the books aren't anything to praise but they also weren't so in-your-face emo.
Queen of the Damned was embarassingly terrible. Everyone involved in that film should issue a public apology. I looooved Interview with the Vampire, it actually follows the story and the characters are all exact (except for Armand...wtf happened there) but WHY DID LESTAT HAVE BROWN HAIR in Queen of the Damned? And Akasha is supposed to be really pale...like all vampires. Just. Ugh. That one may actually be the worst adaptation I've seen.
Oh, and the new Conan is terrible; way to rape the character, Hollywood.
Burton's Alice in Wonderland was bad too. I know it wasn't a direct adaptation but I don't care, don't use the name of a book if you aren't going to follow it.
Percy Jackson was reeeallllyyy bad and I didn't even read the books.
On a happy note, the Game of Thrones tv series is fantastic.