I saw this last night and honestly, I was just blown away. It's hard for me to imagine any production of "Cabaret" that isn't the Mendes vision, but from the second your ticket is scanned you're just in another world and it sort of forces you to forget everything you knew about the show. My email said to arrive an hour early which I thought was a bit excessive but I did anyways and I'm very glad for that. You're taken through "tunnels" backstage and up and down stair cases in differently lit corridors which really make you feel like you're both in an underground setting and also completely turn you around, knowing where you are. The comparisons to "Sleep No More" are appropriate in the sense that there are musicians and performers who perform in different areas and you can follow them to their next "area" or stay where you are. I followed a few out to the main area (which, looking around I realized after a half hour was actually the usual main entrance) where we were treated to an insane (in a good way) dance performance, followed by a "the house is now open" announcement. Those same performers appeared in the Stalls and also where I was in the Dress Circle (not sure about Upper Circle), playing music and "dancing" until the show began. For 40 minutes or so there was ALWAYS something to watch around you.
As for the performance, I thought it was just overall spectacular. Eddie Redmayne is a totally different Emcee than I've ever seen and for that, I was grateful. Because of the staging there was really no place for comparison to anyone else - I think Rebecca Frecknall can take as much credit for that as Redmayne, really. Jessie Buckley's Sally was a lot different than I expected. Having read about her manic performance, I suppose they've decided to tone it down a bit and she was a lot softer in places that I'd heard she was "manic". Her performance of the title song was very strong, I thought and struck just the right balance of sadness and anger that she brought to her Sally. Sally is one of the most interesting characters in all of musical theater to me. It can be played a million different ways and really, none of them are wrong. She can be played as Happy, Sad, Depressed, Angry, Bitter, the list goes on and they can ALL work.
As for talk of Broadway, I can't see how this could work anywhere without the same "Underground Berlin Nightclub" experience they have here. The show looks and feels expensive and lavish and that would all have to find a way to transfer with it. Is there another theater that would (right now) completely renovate itself for a show? Much like the Roundabout production, this one feels like it was built to last - it's not going anywhere anytime soon.