Since its debut on February 15, 1942, "The New York Times" has been presenting its readers with the ultimate in crossword puzzles and has established itself as an icon of American culture and leisure. Puzzle clues are delectably clever as well as challenging. Solving them can be joyful, maddening, and always broadening. "Times" crossword aficionados know that the Monday puzzle is the most readily solved, relatively speaking. But don't let it fool you. As the week goes on, the puzzles grow more difficult--and the satisfaction in discovering the mystery behind each clue grows greater, too. Every puzzle overflows with surprises, learning opportunities, and just plain fun.