This might have been absolutely hilarious had I not read all the spoilers beforehand. Now, my reading experience was an odd mix of second-hand embarrassment and awkward laughter. There are some heartwarming bits of dialogue towards the end of the play, but overall The Cursed Child neglects both the inner logic of the Harry Potter universe and the figurative magic of the original series. 
 Enough has been written about the terrible plot, so I'm not even going to touch that, but 
 there is one thing I really missed reading The Cursed Child, and it's not my childhood, although after this I'm a bit afraid to read the books again. (What if I'm just too old and the nostalgia has worn off?) (Nah, just kidding. Won't happen. ANYWAY...) It is particularly the worldbuilding that always made the Harry Potter universe so appealing to me: the epic quest to save the world comes second after all those fanciful details of witches' and wizards' everyday lives. Of course, dialogue-driven drama can only do so much, and perhaps I should see this one on stage before making a judgement, but worldbuilding-wise The Cursed Child offers little new and makes the foundations of what has already been established crumble. 
 On bad fanfiction scale, 5/5. On "I'm supposed to take this as canon" scale... what the hell, Rowling?