I went on the first week - and it was very nice. They have costumes (Idina's black dress, Kristin's opening dress, Joel's wizard outfit, and others), props, photos, masks, a set design model, etc. upstairs in the lobby area for you to walk around and view. A couple of cast members conducted the tour - and spoke about some of the things in the lobby. Then they took us into the theater and shows a video (as they talked a little bit about the show), and then they conducted a question/answer session afterwards. The question/answer thing was very interesting (I guess depending on what questions are asked!), but I learned a LOT about how the show is run, what happens behind the scenes during a performance, etc.
I would highly recommend taking the tour - it was incredibly interesting.
It would have been nice to go back, but with the large group of people I'm guessing it would be tough to manage taking everyone back (I've been back there before and there never would have been enough room for us all to fit comfortably.)
Also, those hoping for a "making of" film with original cast members will be disappointed. It mainly features clips and interviews with the touring cast (Stephanie and Kendra, etc) and the creative team -- with very few clips of the broadway cast (in fact, I don't remember if there were any at all...hmm.....)
"I never had theatre producers run after me. Some people want to make more Broadway shows out of movies. But Elliot and I aren't going to do Batman: The Musical." - Julie Taymor 1999