(I realize the play is performed without an intermission, and the transition between the two sections of the play is even very seamless, but I'm using the terms "act 1" and "act 2" because that seems to be how the play is structured)
I thought the first act, with the children, was utterly fascinating. But for me the play really lost steam when it jumped forward in time. What started as mysterious and layered suddenly turned into a really average, run-of-the-mill family drama. The adult siblings bickering and wallowing in their family issues is something I feel like I've seen all too much of onstage in recent seasons. Yes, there is some payoff to what we had seen before, but I feel like a lot of it could have been filled in by our imagination, and for me there was too many "wink-wink" bits of reminiscing about things we saw in Act 1. I also feel like the air of dreadful mystery surrounding act 1 was stripping away when all of the answers to our earlier questions were spoon-fed to us in Act 2.
Ultimately, while I absolutely didn't hate it, it was really frustrating to be so entranced by the first chunk, only to have it lose me in the 2nd.