An eighth Harry Potter story. At best, this sounds too good to be true. At worst, it sounds like a misbegotten cash-grab. Add to that the fact that the story was to be a play, not a novel or a film, and you have one of the most eyebrow-raising announcements in recent memory. So is "Harry Potter and the Cursed Child" a worthy addition to the wizarding canon, or a complete dud? I'd have to say it falls somewhere between those two. I'll stick to mild spoilers only as I explain, but if you're determined to be completely surprised, I advise you to go in blind and form your own opinions. The book/play is definitely worth buying.
First, the bad. I don't really understand what's become of J.K. Rowling in recent years. She transformed the literary and cinematic realms with her Potter books, pioneering fantasy trends that continue to this day. I suppose she's trying to make stage plays more popular now? Not sure if that will take off, and it's kind of unfair for the many fans who can't afford to go see the play themselves. Those people are stuck with reading the script, which requires a lot more imagination to really enjoy. There's very little of Rowling's great descriptive prose on display, mostly just dialogue - and it's unclear how much of that was actually written word-for-word by her personally. It sounds like her style; I'll say that. But reading it definitely pales in comparison to reading an actual book. Frankly, I'm disappointed that Rowling hasn't taken the time to flesh this out into a novel. The same goes for the other Potter-related fiction she's written lately - the pre-Fantastic-Beasts pieces on Pottermore, to be precise. It's like reading pitches she hasn't bothered to turn into real books. Obviously, when you're as famous as Rowling, you can get away with posting your world-building notes online or having somebody else turn a story idea into a script and still have millions reading the stuff...but it smacks of laziness on her part, in my opinion.
Also, if you come to this book hoping for a new era of Harry Potter, you're going to be disappointed. This book is an epilogue to the original series, not the start of a new one. There's nothing ground-breaking. The mythology is not expanded, and the new characters spend most of their time dealing with the legacies of the original cast. I'm gratified that the wizarding world will be built up by the Fantastic Beasts film(s), but there's a lot of untapped potential in the modern Potterverse that isn't even touched in "Cursed Child".
So, basically what you've got is a skeletal "tribute" story that's not quite meaty enough to qualify as an eighth Potter book. What is there left to like, then?
What makes "Cursed Child" work despite all the strikes against it is what it does with the aftermath of the original stories. If "Deathly Hallows" had to have a follow-up in the first place, then this is a surprisingly good one. It's certainly an improvement on the frequently-criticized, rushed epilogue to "Hallows". This is basically an expansion of that last chapter, exploring what it's like for Albus Potter to grow up dealing with his famous dad's legacy. And it's very believable in that respect. True, Albus doesn't come across as likable until near the end of the book, and even Harry shows some striking flaws as a father. But given where both these characters are coming from, these problems make sense. It's not the forced "happily ever after" of the Hallows epilogue; it's complex and realistic. Plus, there's a very sympathetic, funny character in play in the form of Scorpius Malfoy, Draco's son. He ends up stealing the show, and is arguably the hero of the story in his own right. His lines made me laugh out loud more than once, and convinced me that to whatever degree Rowling was involved in writing this story, she's clearly still "got it".
The story, once you get past the awkward format, is gripping - I devoured it in one afternoon. There are quite a few surprises in store for hardcore fans. And on the whole, the tone is very appropriate for those who have "grown up" along with Harry. Fans who are now adults can relate with the themes explored here, even when characters mess up pretty badly. Harry certainly made plenty of his own mistakes over the years, and occasionally acted like a jerk. So I'd argue that it's worth giving Harry's progeny a chance, even if you don't take to him at first. At the very least, read it for Scorpius. I'm not saying you definitely won't be disappointed, but there are far worse ways for a Potter fan to bide the time until Fantastic Beasts gives us a more weighty addition to the Potterverse.