Two things leaped out to me.
First, Tony Shalhoub is absolutely wonderful in a tour-de-force performance playing three roles. As the adult Moss Hart looking back on his life as the main one of the show's narrators, as Moss Hart's father, and...most impressively and cleverly -- as Hart's writing partner, George S. Kaufman. He's great in all three, each of them separate in style from the other, but stands out most as Kaufman.
And second, Andrea Martin blew me away. I knew she had won two Tony Awards, but those were both for brassy comedic parts, the kind I knew she did so well. But here -- and she, too, plays three roles -- she shows a range and a tenderness and a depth of emotional drama and, of course, comedy that was a revelation. She's utterly great.
Not to leave him out without mention, Santino Fontana is excellent as Moss Hart as a young man, occasionally narrating, but mostly playing him within the dramatic core of the story. Good as he was, though (and he was very good), it's just that Shalhoub and Martin gave performances that were special.
The show received five Tony Award nominations, including one for Best Play and one for Tony Shalhoub as best actor. (That Andrea Martin was passed by for supporting actress I can only attribute to an excessive number of brilliant supporting actress performances that year, either that or a collective brain freeze.) It won one Tony for set design, which is integral to the show, almost as a character.
If you didn't see it, here it is below. The show runs 2 hours and 19 minutes. If that's too long for one sitting. Act One has two acts. The first ends around the hour and 7-minute mark, so split it into two. Or at least just watch some of it.