I'm always over the moon happy when I hear about one of my favorite books being optioned for TV or even a movie. But yeah, as the naturally critical person that I am, I almost always end up absolutely hating what they did to my poor fictional friends. Here are some of the worst book-to-movie adaptations I've ever seen.
(based on VAMPIRE ACADEMY by Richelle Mead)
Starring: Zoey Deutch, Lucy Fry, Danila Kozlovsky
I do love the idea behind all this and on it's own it's a great and entertaining film - BUT HAVE YOU READ THE BOOKS? The movie is a teen comedy whereas the novels are dramatic, full of angst, and indeed sometimes hilarious.
I wish they hadn't focused on the hilarity part. The movie is a try-hard slapstick comedy that's really okay, but nothing like the book. They did follow the plot sort-of-closely, but the outcome is just nothing but a teen flick. It's not a bad film, but it's a godawful book-to-movie adaptation.
The main couple, Rose and Dimitri, Romitri - they have maybe 2 scenes together before they confess their undying love to each other. Why, just why? At least the casting was alright.
City of Bones 
(based on CITY OF BONES by Cassandra Clare)
Starring: Lily Collins, Jamie Campbell Bower, Jonathan Rhys-Meyers, Lena Headey
For fans of the book, this adaptation was like a slap in the face. Starting with terrible casting and two lead actors who have the chemistry of two wet noodles, it just wasn't meant to be.
The book is insanely complicated and trying to cram this into a decent length novel was just bound to end in failure. Even more so, because whoever wrote this catastrophic script decided to spoil story lines from the sequels along the way. Simply because they could. Ugh.
(based on THE HOST by Stephenie Meyer)
Starring: Saoirse Ronan, Max Irons, Jake Abel, Diane Krüger
I absolutely loved the book but I hated the movie. There was so much unintentional situational comedy in this that I couldn't help but cringe the entire time. The book has a special atmosphere to it and is really a unique read, but in the movie everything was just a mess.
No chemistry, catastrophical casting and more of a love story than a sci-fi book exploring the unique bond between an alien and a human, forced to share a body.
Hollywood was like: "HEY there's a love triangle let's just cast two hot hunks and the script will write itself!!"
(based on INKHEART by Cornelia Funke)
Starring: Brendan Fraser, Eliza Bennett, Paul Bettany
I think we can all just universally agree that this is the most epic fail of book-to-movie adaptations within the last few years. INKHEART was one of my favorites growing up and I don't even want to get started listing all the things that is wrong with this because it's just too painful to remember.
But hey, at least they got Brendan Fraser to play Mo, Funke actually wrote the part for him, so that's nice. Thank god there won't be any movie sequels in the near future of this atrocity.
(based on THE PRINCESS DIARIES by Meg Cabot)
Starring: Anne Hathaway, Julie Andrews, Mandy Moore
The biggest and most awful epic fail in terms of book-to-movie adaptation to me. Hear me out - THE PRINCESS DIARIES is my favorite book forever and always. If you've actually read it, you do know that pretty girl Anna Hathaway has absolutely nothing in common with Mia Thermopolis.
Of course the movie on its own is entertaining and even good, but if you know the insanely good book, the hilarity of Mia, the wonderful creepiness of her Grandmère and the brilliance of her father's terrible awkwardness, you would think the same way. With the movie I got cheated out of almost all the things I loved about the book.
With the movie, we got a mediocre easily forgettable hollywood romcom that could have been so much more. The book is not about romance, it's so not just the journey of an ugly duckling becoming a swan. I'm just insanely frustrated with this.