Had to sit on this for a bit, and even checked out the script from the library afterwards to give it a re-read, but I actually liked this quite a lot.
Probably the biggest surprise is that it seems to posit that Dahl wasn't so much a pure-blooded antisemite as he was an insecure, paranoid bully desperate to use any tools he could get his hands on to force the people around him to prove their devotion to him. The ending, in particular, grabbed me, not because of the nasty and apparently verbatim language he used, but because he's overtly doing it as a way to challenge his wife. "Would you still love me if I stabbed you?", basically, and we know that she would, because we know that she married him. It's an ending straight out of one of Dahl's own stories.
Lithgow does give a terrific performance that really elevates the text and I was extremely entertained watching him constantly ferreting out and exploiting weaknesses. This is essentially a play about a group of people cornering a rat, which is an odd dynamic and I can understand why some would find it repetitive or static. Certainly, it absolutely does not (in its present state) necessitate two whole acts, and would probably work better as an 80-minute one-act. People keep being shuffled in and out of the room, and the use of the two servant characters felt particularly uninspired.
The process by which provocateurs become lonely, hateful monsters (often seeming to beg for external judgement) is fascinating to me, though, so I think I was primed to enjoy this. I was also intrigued by the differences in viewpoint between the American and British Jewish characters. When Jessie asks Tom where he would go if Jews were banned from England, he blithely replies, "Provence", which feels like a pointed criticism of the way that Americans isolate themselves, and how it leads to a hysterical and apocalyptic mindset. There's an intriguing subject to be explored there.