What is most striking about this film are the performances by the leads. I've grown up taking for granted the fact that Jack Nicholson is a great actor with only a few of his contemporary performances serving as meaningful evidence, but here, in his younger days, Nicholson proves to be a master of smarmy, sleazy subtlety. Jessica Lange is at times vulnerable and at others succeeding in her attempt to be blisteringly alluring. The film's "love" - or should I say animalistic fucking - scenes also serve as the film's appeal, but I found myself more repulsed than aroused. Finally, David Mamet's script is quite strong, but this is not the Mamet of Oleanna and Wag the Dog. Rather, this is the Mamet of The Verdict, a Mamet who relies on subtext more than acerbic dialogue. For example, he writes, "I'm tired of doing the right thing." Pause. "They hang people for that, Cora." It's up to the actors to imbue these lines with meaning, and these actors are up to the task.
The film's flaw is the storyline. At the end, we wonder what the film is saying about these characters. It seems that they reach their conclusions out of moralistic fatalism, not out of any authorial or directorial intent. Compare this film to There Will Be Blood, which deals with many of the same themes sans sexuality, and you'll find that Paul Thomas Anderson has a clear vision and feeling about Daniel Plainview, but the same can't be said of these characters. What is more, there is a short subplot with Anjelica Huston, and in the words of Roger Ebert, she seems "to be visiting from another movie."
Overall, if you can look at this film as a collection of scenes from an acting class and divorce yourself from the need of a consistent story, The Postman Always Rings Twice is a good film.