In the Sixties, few acts had as many hits—or sounded as unique—as the Four Seasons. Leader Frankie Valli boasted a once-in-a-lifetime voice with a three-octave range and an unstoppable falsetto reach, while his bandmates teased out precise doo-wop harmonies on tunes such as “Sherry,” “Walk Like A Man” and “Big Girls Don’t Cry.”