Cursed Child was somewhat of a disappointment. Let's just get that out of the way. I know you haven't gotten my full opinion on it yet (the video has yet to be edited), but it was. The only reason I don't call it a massive disappointment is that I went into it with plenty of caution. I was prepared for the let down.
However, since I'm still not quite ready to accept Cursed Child as Harry Potter canon, I'm not calling it my least favorite Harry Potter book. No, that award goes to a book that, despite any faults, is actually well written and that, funnily enough, ties into the play quite well: Harry Potter and the Goblet of Fire.
I remember reaching the fourth book (the last one out then) as a kid and stalling in my reading progress because I was bored by the first chapter. Now, it's possible that the book's length caused me to pause at that age, but considering my feelings on the book even now, I think there's more to it than that.
Quidditch is great. I do love Quidditch to a certain extent, but I was never thrilled to be reading about a Quidditch World Cup. Then there was the Triwizard Tournament. I guess I'm just not someone who's that interested in reading or watching about competition when it's any sort of physical task. It didn't feel like what I wanted in a Harry Potter book either, and I think that is a large part (if not the only reason) that Goblet of Fire is my least favorite book.
It's not that Goblet of Fire is a bad book. We're not talking about something on par with Cursed Child here. It just contains a lot of storylines that aren't my cup of tea.
(Of course, now that I'm writing this, Hunger Games came to mind, which is about a competition and which is a book I love. I think the difference is that the competition in The Hunger Games is inextricably tied to the story. You can't have the story without the competition. I believe the fourth Harry Potter book could have been written without the Triwizard Tournament. Because the tournament was there, it became tied up in the plot, but it wasn't necessary if J.K. Rowling had taken it out and written the story a different way. I think that's a fundamental difference.)
I know I'm not alone in seeing the fourth book as my least favorite, but I'm not quite sure if one book leans towards being the most disliked. So, I'm curious, which Harry Potter book is your least favorite?