Two thirds of this show was a hot mess express, and the remaining third was compelling and frustrating in equal measures. There's an interesting story in there about people stepping aside as evil rolls through, but they spent a quarter of a century working on this show and the best they can do is bring it to a simmer for about twenty minutes.
As for what works, Sussman's lyrics were quite good, very solid and punchy, and a lot of the musical numbers had a kind of shapely muscle to them that I appreciated. The sequence at the end, where Rabbi accounts for how all of the other members of the show passed away (some immediately, some over time), and reconciles with being the last one alive, and the one who has to remember, was also very moving.
Unfortunately, the rest of the show is just...this and that. Putting Zien front and center means we get lots of Zien, which is wonderful, because he's up there acting his heart out and doing his best to sell the stale zingers he's been saddled with. However, the memory-play aspect feels incredibly tacked-on, and his function throughout the evening is muddled, which means the epiphany and closure he receives at the end feel disconnected from the rest of the show. For too much of it, he's just doing antics and occasionally going into hysterics.
It also means that the Harmonists themselves get almost no room at all to be developed as characters, to the extent that I honestly couldn't identify them individually in a lot of scenes until the dialogue informed me, and even then, who are they? Why, for example, does Bobby want to go back to Germany at the end of the first act so badly that he gets a big impassioned number about it? This element of his character seems to come out of nowhere because he's spent the entire first act as That Guy #4. When they all get their send-offs at the end, I knew almost nothing more about them than I did at the start of the show.
As a musical, it's mostly a mess, though I Will say that "And What Do You See" and "Every Single Day" are both genuinely very good (the former in particular is extremely good at developing Mary's point of view). The rest struggle in some way or another, with many of them feeling their age (they could be cut songs from his two Don Bluth scores), and to me, Manilow has a tough time building on his initial melodic themes. The most obvious example is "Where You Go", where Manilow's deviations from the original Chopin are like a dated, tacky extension to a classic building, but you also have the comedy numbers, which are weighed down by pounding repetition.
None of this is helped by the book, which makes a lot of baffling structural choices (the Josephine Baker number??) and saddles the actors with leaden, lumpy dialogue. They do their best with it, and the production itself is fairly slick, though the neon floor tape is unfortunate. It's a shame those lightbulbs at the very end couldn't stick around for longer, it produced the same effect as some of the Kusama mirror rooms, and I do kind of wonder if Borritt reverse engineered the entire design to get to that moment. However, the overall visual sense of them being lost in this glossy, black void felt appropriate.
I think the best thing about this show is how, much like Glazer's Zone of Interest, it feels like an overt call to action, even if both works focus on an extreme example. I still think "would you have killed Hitler?" is such a hoary chestnut that it's hard to take entirely seriously, but regardless, I never thought I'd see an overtly pro-assassination musical. Tasking the audience with considering how they might stop events, if they would give their lives to halt a train of unimaginable cruelty, is a highly respectable goal. If they'd found a better way to center the show around exploring how people step aside, this might have cohered, but it's so all over the place up until the end.
Also, though Zien does a great job of massaging Threnody into a functioning number, Nathan Lane singing Betrayed will forever be imprinted over it for me.
