A lot of great books become okay movies (Ella Enchanted), and some become really great movies (The Princess Bride.) A few become horrible, weird disasters that are not recognizable as the books we love. A lot of these adaptations are young adult fantasy, partially because so little effort goes into making media for young adults and kids. Here are some movies that were face-palmingly disappointing. Of course, the people who worked on these movies worked hard and are human beings, but we can critique the films without being too critical of the people who made them happen.
The Percy Jackson Series
It is almost universally agreed within the fandom that the Percy Jackson movies were terrible. They even made a second one despite the horrible reception the first received, in an attempt to save the franchise. The biggest mistake this movie made was taking the heart out of the series. They aged up the characters in order to sell the movie to teens, and instead of sticking to the source material, made cheap jokes about sex and used a lot of expensive visual effects. While a lot of books don’t translate well to the screen, Percy Jackson could have been amazing. It could have been on the level of Harry Potter as a film series, if it was done right. It literally would have been better if they had a robot voice read the text of the book and had the only visual be the Microsoft screen saver. Even the author publicly repudiated the movies. Zero stars.
Divergent
The Divergent series has a lot of issues- and we won’t get into those now, but the movies were a huge flop. They did not even complete the series, which gives you an idea of how poorly they were received. The studio kind of got in over their heads by splitting the last book into two films. The last book was pretty bad, and while the first movie didn’t divert much from the book, it only exposed the weaknesses inherent in the book. One of the central facets of the book was the love story, which was wooden in the movie. It doesn’t help that the male lead looks about ten years older than his costar. As movies go, I’d skip these ones and save a couple of hours.
The Mortal Instruments
While Cassandra Clare’s popular series is a byzantine, magical journey, it’s also kind of a crazy ride. Some of the source material didn’t exactly translate well to the screen (incest, but not the real kind.) The movie flopped, and then there was a second attempt with a TV show, which hit a lot of the same beats without fixing the inherent issues (too many characters, too much plot, too much explanation.) While Clare has continued writing her books, it’s probably safe to say that they won’t be making their way to the screen any time soon.

Me trying to make sense of this movie
Vampire Academy
Admittedly, this movie is only really bad if you read the books. The books are kind of dark, emotional, and intense. The movie is a campy comedy, with romantic subplots. It’s mostly disappointing for fans of the books, which are much deeper and more complex than the movie, which basically just makes vampire jokes for two hours. It’s kind of a fun, silly thing, but it’s barely recognizable, with the exception of the book’s basic mythology and characters. Like the Percy Jackson series, there was a lot more source material, but further films have not metastasized. It’s just disappointing that the studio beefed it on what could have been an epic saga. They also un-ironically subtitled this film Vampire Academy: Blood Sisters, which is so menstrual that it has to be on purpose?
The question remains: why are all of these excellent books being butchered to make movies that barely recoup their costs? To my mind, the answer is twofold, and fairly straightforward. Firstly, movie studios think that they can make a quick buck if they make films even vaguely based on source material that is popular. They think that people who liked the book will go see the movie on principal. Even if you go to hate-watch it, they still have your money! Secondly, Hollywood thinks kids and teens are stupid, or at the very least, not demanding. This is wrong on several levels, but believing it means that they can write lazy movies with bad casting on the assumption that people will watch anything. To some extent, they’re right. Mortdecai made 47.3 million dollars. Some people will go see anything, once. However, if you have a viable franchise, and you throw it away for a cash-grab, people aren’t going to come see the next one. That’s why all of this is so disappointing, and such a waste. These are decent books, some of them are brilliant, and they deserved better than they got. Studios have proved that they can make great movies for teens and kids, they’ve just decided not to try. Two thumbs down for effort.