This book has made me feel about 1000 different ways, each of them conflicting with the others. It has both confused and thrilled me on some level, and now I'm sitting here having no clear idea how I feel about it. It's not great, it's not terrible. It's neither necessary or unnecessary. It neither furthers the story of Harry Potter nor harms it. It just kind of... is. 
 It's hard to really be disappointed in this book. We weren't supposed to get any new Potter material, so it's not like our expectations were set very high. Rowling basically promised at one point that there would never be another Harry Potter book written by her. And in a way, there still hasn't been. Her touch is definitely on the plot and characters, but this is much more of a Jack Thorne play than it is a J.K. Rowling novel. As such, the writing style and restrictions of a play have sucked a lot of the life out of the story. 
 Also, reading this as a play confounded me a little bit as a fan of theater. It has SO MANY SCENE CHANGES. I can't imagine what this thing must look like on stage, but it must be chaos. It has as many scene changes as a movie, with very few of them lasting more than a minute or two. It almost feels like they wrote it as a movie first, then decided to make it a play after the fact, without adapting much of it to the stage. I don't know, maybe it's a great play, but it seems unwieldy as hell. 
 Anyway, the story itself. It's fine. There's a decent development of the relationship of Harry and his youngest son, Albus, and it's nice to see where all of the Potter crew ended up decades after the Battle of Hogwarts. But, this play is almost exclusively about the big, crazy, magical plot, and as such leaves a lot to be desired in terms of character connections. People spend most of the play stating their emotions and desires out loud rather than actually feeling or acting upon them, mostly because there's not time to really live in any of these incredibly short scenes. 
 I found it very hard to care about anyone in this story. The best plays are all about relationships, about how people affect each other, usually very deeply. This play is about a series of magical errors and the attempts to fix them. The relationships it does contain are mostly surface-level, well-trod types: father-son, best friends, husband-wife, and never really explored beyond those simple starting points. It doesn't feel like any character truly grows or changes or realizes anything about themselves because of the story, it just kind of feels like these changes were written in because they're expected to happen. It's ultimately kind of lazy. 
 All that said, the plot I'm complaining about is kind of fun. It's got a lot of big, Pottery energy and twists and magic creatures and all that. There are some pretty huge logical leaps you have to go along with, though, and they kind of hurt the story. I won't spoil anything, but I'll just say the way the story progresses kind of contradicts itself and makes it very difficult to suspend disbelief, and the plot in the latter quarter of the book or so suffers for it. 
 So, I'm not making this sound very good, and I honestly don't think it IS very good. But, it has enough going for it with Rowling's involvement and its lighthearted tone, plus it's a quick, decently-fun read, that I still think it's worth the very small amount of time commitment. I also think someday it will make a great blockbuster movie, assuming they smooth over a few of the weirder plot problems that seem fixable. Here's hoping they don't make it a trilogy.