Mild spoilers below.
This does not read like Harry Potter. I realise it’s a rehearsal script and therefore about a third of the whole thing, I know theatre is a completely different medium of storytelling than literature, I suspect the text comes alive on stage thanks to the actors’ talent, the props, the music, the special effects, the director’s vision and is probably completely transformed. I appreciate all that and thus can’t honestly diss the text as subpar.
So all I can say about it is it wasn’t that pleasurable a read. The writing is not great, the characterisation, as glimpsed only through the characters’ lines, is completely off for most characters (not that people don’t change as they grow older, but HP is full of compassionate, brave and adventurous adults, whereas The Cursed Child is populated by various, albeit milder, versions of Vernon Dursely) and I found the plot to be both cheesy and not very convincing, not to mention the numerous deus-ex-machinae and convenient strokes of inspiration.
The emotional impact was very low for me. I could hardly recognise any of the characters and their lines were almost embarrassingly bad at times – awkward, unnaturally worded, nothing like they sound in canon. Everything is solved way too easily, the central personal conflict is rather light, the „cameos“ of old characters felt somewhat embarrassing to me, like they were paraded with the sole purpose of pleasing hardcore Potterheads, and I’ve always detested fan service. The guest appearance of Severus Snape, as much as I loved seeing him on page again, was especially grating, as he undergoes a complete (and terribly corny) character makeover in the space of 3 pages.
Furthermore, I have an old distaste for the topic of time travel. I’ve yet to read/see it done well. It inevitably creates glaring plot holes, as it does here, and leaves me dissatisfied. This isn’t a big deal though – I’d read anything in the HP universe, even if it’s about Moaning Myrtle time-traveling with Peeves to play pranks on several generations of Hogwarts students. It does sit a bit cheap though, like there wasn’t a good enough story in a new setting in the Potterverse so they decided to rehash the old ones. It feels like cheating, like these well-known and beloved stories are used as emotional stuffing because the authors know the original story can’t carry the play by itself.