"Mr. Mamet's talent for burying layers of meaning into simple, precisely distilled, idiomatic language - a talent that can only be compared to Harold Pinter's - is not the sum of ''Glengarry Glen Ross.'' This may well be the most accomplished play its author has yet given us. As Mr. Mamet's command of dialogue has now reached its most dazzling pitch, so has his mastery of theatrical form. Beneath the raucous, seemingly inane surface of ''Glengarry,'' one finds not only feelings but a detective story with a surprise ending. And there's another clandestine story, too, bubbling just underneath the main plot: Only as the curtain falls do we realize that one of the salesmen, brilliantly played by Robert Prosky, has traveled through an anguished personal history almost as complex as Willy Loman's.

So assured and uncompromising is Mr. Mamet's style that one must enter his play's hermetically sealed world completely - or risk getting lost. "

---Frank Rich, New York Times 3/26/1984