I couldn't grade this on my usual novel scale, what with it being a rehearsal script typed up by someone only casually acquainted with proper punctuation and sentence structure. Maybe all scripts are like that. Having no experience with them beyond the occasional Shakespeare play, I have no idea. My rating reflects my enjoyment of the story itself, which is basically a rehashed time travel plot with a few holes in it. If it was just called "The Cursed Child" and all the names were changed, I'm not sure I'd recognize these characters as JK Rowling's creations. Except maybe Scorpius. He rocks. If the kids cast as him play their cards right, he'll steal the show every time.
I thought it was cute and entertaining to read, but I'm sure it's absolutely enchanting on stage. (See what I did there?) Now if only London wasn't on a different continent. In a different hemisphere. Sigh.