This was my favorite Harry Potter book while originally reading the series. I have probably read it close to ten times over the last twenty years.
This is the point where the series starts to turn a little darker. The characterization of Lupin and Sirius adds so much depth to the series and begins to beg the question: can our heroes, the people we look up to most, have flaws or make mistakes? The big bad evil guy is no longer just some vague children's story villain. We begin to understand just how Voldemort has torn families and friends apart and how some witches and wizards chose Voldemort's promise of power at the expense of their friends' lives.
Every time I reread this book I am caught up in Harry's overwhelming sense of hope near the end of the book and I have an absolute crying fit afterward. Few scenes affect me like the scene where Harry is returning after visiting the inside of the Shrieking Shack and what happens on the other side of the Whomping Willow. The turn from unparalleled hope to devastation gripped me like no other scene had ever before and it's become a benchmark by which I measure the emotional effect of books.
I watched a youtuber blind react to this book when I was finished reading. It was wonderful to live vicariously through her first time experience with the book. Although the emotions I experience while reading this book have faded with time, they are still strong each time I reread it and it is always a treat.