I saw it, it was great! It's very faithful to the original Roald Dahl book, and it's funny, totally twisted, and very sweet.
The cast is incredible. We saw Milly Shapiro as Matilda (there are 4 girls sharing the role who alternate at each performance) and she was amazing - and so tiny! Milly is 10 years old, but Matilda is only 5, and she still totally looked 5 on stage. Bertie Carvel is hysterical and completely terrifying as Miss Trunchbull, and the couple who play Matilda's parents are also really horrible and hysterical too. Like I said, it's a really twisted show!
But it was awesome. My mom liked it so much that she just got tickets to see it again so she can take my dad can see it.
Have a great time!