What is the author's style in Glengarry, Glen Ross by David Mamet?

Mamet is very clear about what is important in his plays. In one of his essays in Writing in Restaurants he points out that it is not the theme of the play to which we respond, but the action. In another essay in the same book he points out that "good drama has no stage directions. It is the interaction of the characters' objectives expressed solely by what they say to each other not by what the author says about them."