This general comment about drama, which occurs on page 84, jumped out at me:
It is as close to being a total art as the race has invented. It can tell, like science, what is-but more, it can tell what ought to be.Emphasis mine. Miller is usually thought of as a naturalist, but here you can see his idealistic side coming out. Without that idealistic side, I don't think he would have kept all those theater seats filled all those years.
If you fall to mere reporting
In your play-writer position,
You'll soon see the crowd resorting
To fleeing at intermission.