I am writing this in hopes of saving someone else a ridiculous amount of money and time, since it's too late for me.
If you hate Harry Potter... don't see this. If you love Harry Potter... don't see this. If you have a weird penchant for plays written so badly you'd be forgiven for thinking an AI penned it, and then sold it to a school amateur production to perform with a West End budget... okay maybe this is for you, and only for you.
The script is AWFUL. I'm saying this as kindly as I can. If you don't believe me, borrow it from your local library, read it and THEN decide if you want to sit through SIX HOURS of whiney Harry, one-dimensional Ron, "I can only be accomplished if I have a man by my side" Hermione, and whatever the hell the Trolley Witch is supposed to be. But wait, there's more (spoilers ahead in this paragraph)! Many of the scenes are bizarre in a way that would shame fan fiction. There's a scene in which a painting of Albus Dumbledore and Harry Potter proclaim their love for one another (paternal, of course, but even this is WEIRD). In another, Albus Potter (it's confusing, I know) tells his aunt he wants to have a baby with her and snogs her (don't worry, he's on polyjuice potion, so it's FUNNY not horrific!). And best of all, you've got Hagrid, who starts off delivering his lines in a truly odd monotone and ends in an American accent, for some reason.
The stage sets, which at least you might think would be spectacular, are just a series of moving staircases and archways. The special effects are cool, but they cannot singlehandedly rescue a show which, may I remind you, is SIX HOURS LONG and insanely expensive.
There are some performers who try their best. Scorpius is adorably innocent and wholesome. Moaning Myrtle is hilarious. Snape tries to stop the storyline from derailing, but unfortunately isn't onstage long enough to be successful. Umbrage is deliciously despicable.
There are so many brilliant shows on the West End. If you think you want to spend a lot of money on this one... no, you really, really don't. Go see the Lion King. Go see literally anything else. You're welcome.