I've seen it!
Saw it in London in May of last year.
I *hated* it.
The stage itself though was the coolest thing I've ever seen. It was incredible - it rotated and split into multiple levels to create mountains or valleys or, say, the walls of Mordor. The costumes were gorgeous too - the production values were simply through the roof for that production.
But the play - say it with me - suuuuuuuuuccked
It completely butchered the storyline of LOTR to the point that it was utterly incomprehensible. The entirety of The Two Towers
was enacted in a 5 minute abstract dance number - I'm not joking. The dance began with the forging of Saruman's army and ended, 5 minutes later, with their defeat at Helm's deep. The next scene, as I recall, was Frodo and Sam crossing the plains of Mordor.