Don't you love it when a book is so wonderful and amazing, that it's left a giant sized hole in your heart once you have finished it? I know I do, maybe I am a masochist or something, but I enjoy it when a book is so lovely that leaves behind an enormous black, empty hole in your heart which makes you feel that nothing will ever be the same because the book is over and there's nothing left to read about that particular series/novel. So yes I enjoy that pain, why? because it tells you that the book was a book well read and it was meaningful, in other words it left you with lesson to learn from and many things to contemplate.
So what makes a book so good that it leaves a mark on your heart? In my personal opinion here is what makes an amazing book:
By strong characters, I mean characters that stand up for themselves, as well as emotionally strong. They don't have to be strong throughout the entire story, it could be, for example them finding their way, or they are feeling 'broken' etc. but they don't let that change who they are, for example Lennie in The Sky Is Everywhere by Jandy Nelson.
Characters in general will make or break a book, when I am reading about a character their actions have to be logical and 'real' I want to feel their emotions, I want to feel connected to them and I want to be able to relate to them easily.
The way the author writes a story in my opinion is extremely important, because if I don't like the writing style, I won't like the book full stop. I won't like it no matter how strong the characters are or how much I like them. The writing, same as the characters makes or breaks a story.
What I love in the writing is when it contains lots of metaphors and imagery. Examples of stories that I like that contain an amazing writing style are: All of Sarah J. Maas' books, all of John Green's books, I'm sure there are many others but at this moment these are the books that immediately come to mind and stick out from the rest.
In other words a strong plot. The storyline has to make sense, this particular element of a story is different for every reader as every reader prefers a different storyline. Therefore the plot has to make you feel intrigued, it has to draw you in and it has to keep you invested in the book.