I'm not sure about the rating. I feel like this one deserves more of a 2 stars but I can't do that to a Harry Potter book, can I? 
 I don't want to write a big review because I think lots of people did a fantastic job already. 
 I agree that this story was nice in some ways and it's of course amazing to visit this world and those characters again but it just lacks in quality. I mean it's a play. It's not a book. 
 We don't have the insight we want to get. Everything moves at a fast pacing and the plot is extremely weird and convenient sometimes. Some characters behaviour is disturbing and the whole plot twist (view spoiler)[Bellatrix pregnant with Voldemorts child (hide spoiler)] is absolutely unbelievable. 
 Still, I had fun reading it and I would love to see the play. I can't imagine how this would turn out as a theatre play. 
 Well, this will be the first HP book I won't re-read every year. Sorry but this reads too much like fanfiction and not enough like an actual J.K.Rowling masterpiece. But I'm sure I would watch the play a few times.