There are many books I've given five stars. It almost feels wrong that this one would be just five stars and not so many more. 
Those other books were great and I loved them but I've just never been so - intoxicated almost - by a book. I haven't dared to read a book with lots of pages for years but I'm glad I did because this is hands down the best book I've ever read.
I didn't want to put it down, didn't want the story to end though either. Its topics are very heavy but I thought there were a lot of positive themes in here as well. About love and hope and painful honesty; about friendship and family and choosing your own family.
I don't even know how to explain how much I admired this book. Its characters who felt so real and so lovely (Harold, Andy, Willem, Jude, Malcolm, Richard, so many fantastic characters); the way the story was built, starting slowly and unraveling as you go along in such a mind-blowing way. 
What I heard about this book a lot was how heavy it was and that it was basically made to trigger you. Yes, it was very heavy, but I don't feel like it was done in a "let's emotionally fuck up some people" kind of way (although it did mess with my heart haha). It was written so thoughtfully and beautifully and with so much respect and I just admire this book so much. 

Edit: I read some other reviews (I guess less positive ones, and although they make fair points - the book being unrealistic is probably mentioned the most - I don't feel like it took down my appreciation for this book while reading it.