Mamet presents certain perspectives on acting that are indeed quite sensible. There are aspects that I wholeheartedly agree with, and it's likely that some in the theatre world could benefit from being reminded of these points. However, it seems to me that he has deliberately misconstrued many other approaches to acting, such as those of Stanislavsky and Meisner. He mocks them for things that I don't believe those acting philosophies were actually advocating. In my view, when we look closely, Mamet and Meisner are ultimately aiming for the same thing. It feels as if Mamet is creating an artificial divide between himself and other so-called "methods".
Overall, there are some interesting gems to be found in his work. But it is so intertwined with other elements that I consider to be highly misleading. As a result, I don't think it's truly worth the time investment.