We went to watch Harry Potter and the Cursed Child and it was really neat.
The aspect of the play that grasped me the most, and what really caught me by surprise, was the use of stage magic, something that should have been obvious in hindsight. The long flowing cloaks of the wizards was put to great affect in concealing trap doors, harnesses, props and pyrotechnics, all of which made for a spectacular show. Seeing people vanish or transform before your eyes is so much more tangible and remarkable than watching it in a film. Plus the Dementors were equal parts terrifying and mesmerising.
All told, I'd give it a nine and three quarters.
Actually there was one other moment that impressed me and I'm not sure it was entirely intentional. We, like many others, were sitting in the balcony seats. At one point, one of the characters was raising their hand in a magical gesture (no surprises there) and because they were walking towards and then beyond the front of the stage, everyone in front of us slowly stood up in waves to maintain their view. In the moment it looked like a spell had been cast over the audience to cause them to stand. It was quite remarkable really.