Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Dark
Nailing down the tone of a play can be tough, and it's something that actors and directors struggle with all the time. Play a farce like it's a realistic drama and the production can just fall apart.
With something like True West, it gets even trickier. Shepard's tone is a dark one. There is something ominous about the situation from almost the very beginning of the play, and we get the sense that a happy ending is probably not in store here. So the tone is dark, but that doesn't mean it's dour or heavy. At times, it just means it's darkly comic.
One of the best examples of this is the story about the father and the dentist that Austin tells. If you take the story at face value, it's pretty depressing. An old guy loses all his teeth, he has no money to take care of it in the States, so he has to hitchhike to Mexico to get some shoddy dental work done. He ends up losing his fake teeth, so the journey was all for nothing in the end.
However, the way that Austin tells it can be extremely funny in the hands of a talented actor. It's a dark story, but Austin and Lee both find humor in it:
AUSTIN: So how long you think it takes him to get to the border? A man his age.
LEE: I dunno.
AUSTIN: Eight days it takes him. Eight days in the rain and the sun and every day he's droppin' teeth on the blacktop and nobody'll pick him up 'cause his mouth's full of blood.
(pause, they drink). (2.7.216-222)
It's a dark story that fits the play's dark tone, but it's all the darker if the brothers find some amusement in it.