Not so much a review as that would need to contain spoilers .. more a personal reaction
As I have no intention of giving anything away (#keepthesecrets) even to those who have read the script, this is not a review but a reaction to having seen it yesterday
I will just say that this is a truly 5 star theatrical experience and it is genuinely worth trying to see both parts in one day. It is perhaps a bit dark for the young ones but if they have managed all the films then they'll probably be ok. You kind of do have to have read the books or seen the films to get the whole story but that is not a bad thing - it allows them to fit even more in. The magic and effects are amazing - I just loved the scene changes!
Really, an excellent piece of theatre, I hope it sticks around a very long time (so that some of you can get tickets!)