Weeks later, I'm chiming in to say that this thread - which was mostly critical of Leopoldstadt - made me more inclined to see it, and I liked the candid but polite exchange of views. Moreover, I took the advice about not getting caught up on who everyone is and how they're related. It didn't totally help, because I did try to study the family tree and glance at the Playbill to see who was in later scenes, and it's just my nature. I understood why the play didn't have any sort of break, but I was wishing for one just so I could sort all the characters out in later scenes.
But I found, especially because I was very close to the stage in the orchestra, that some of my confusion about the characters both didn't matter and seemed to serve a larger point. The initial confusion about which characters are Jewish is part of the story. It doesn't matter too much at family gatherings, but little exchanges give away the fact that the family - despite its outward prosperity and Christmas tree - isn't really accepted in Vienna. That becomes more dramatically clear in the second scene, the clash between Hermann and Fritz (two actors, Josh Malina and the chilling Dave Register, playing their roles for only the second time when I saw the play).
For me, and I'm not Jewish (but my wife is), the play worked as interconnected vignettes that told stories both specific and universal to the Jewish experience in Europe. The Merz and Jakobovicz families may be comfortable (at first), educated, and cosmopolitan - but those small and large humiliations are signs that the horrors of the Holocaust didn't emerge from nowhere. Ironically, the Stoppard stand-in character in the final scene was the only one who rang a bit false to me.
But I thought the play was a very powerful work, one I'm still considering since returning from my New York City trip.