There are perks to turning these books into movies; like more exposure for the book, the author, and more people in the fandom to talk about the book with. The downside? Most of the time, the books get ruined. Most people's expectations aren't met which causes them to be angry then in turn, makes them disappointed on how it turns out. But I guess I get it since it's kind of hard to fit a 300+ page book in one and half hours. But still.
Here are some book to movie adaptations that are perfect examples of what they should do and what they should not do for book to movie adaptations:

Flipped
by Wendelin Van Draanen
The first time I watched Flipped, I didn't even know it was a book. So when I found out, I got a copy and I loved it. Everything about it was so spot on - even down to the alternating narratives. It's a really sweet yet short book and they were able to fit it in its time span and still be able to show the progression of the characters and the story. I guess it was easier for them to do so because the book was short, but nonetheless, it was good.

Percy Jackson and the Olympians: The Lightning Thief
by Rick Riordan
This was definitely one of the worst. This was such a HUGE disappointment. It barely gave justice to the book and there were many inaccuracies. I'm not even going to try counting them. It's like the screenwriters didn't even bother reading the book, they just got the key events and made stuff up from there. I know that is what's supposed to happen, but even the little details matter in the book especially to the book fans. Like for these: where's the Ares fight? Why does Percy look like he's 16 or 19 and not 12? And of course, why isn't Annabeth blonde??? Okay I just listed some inaccuracies, (oops) but those are just some of it. The only redeeming factor this movie had was that Logan Lerman was in it.
- Ana Matti