Harry Potter and the Cursed Child is a play about fathers and their children. It is about trying to live up to expectations and resenting those expectations. It is mostly about the burden of family history.
The play format is actually a good fit for Rowling because her fiction is almost entirely dialogue driven anyway. The playwright is Jack Thorne, based on a story by Rowling. I expect someday Rowling's story or notes will be published and it will be interesting to see how much of the dialogue is Thorne's and how much was contributed by Rowling. If it is mostly Thorne then he deserves some praise for capturing the tone of Rowling dialogue.