Variety lists the show as a "play," and it does have a director. And it does take place in a theater.
But apparently the show is mostly Mr. Lithgow telling stories of his family, and of the role stories and storytelling played in his family. The show includes recitations of poetry by Oliver Wendell Holmes and prose by P.G. Wodehouse.
I found this quote illuminating:
...(the play) encourages auds to make their own connection to the material, without demanding that we celebrate Lithgow's life. He grounds the classics by explaining what they meant to his family, but his biography is supporting material, not the solipsistic main event.
It reminds me of the best of storytellers, who disappear behind their stories. And what you are left with is not the feeling that the storyteller had an interesting life, but a connection with the storyteller, who was able to capture some universal feeling (of pride, of embarassment, of loss, of fear, of love) and share it.