It's Plant's wailing, drifting, compelling voice and uninhibited stage presence, along with Page's electrifying musical direction (and guitar playing) that carry [Led Zeppelin]. The mystery of their success is partly in the surprising ways they take to the stage and not let go, as well as their ability—behind the scenes—to write and record with uncanny exactitude and excitement. They have mastered a unique sound: loud, spiritual and mesmerizing.

Robert Smith, "Robert Plant, Male Vocalist of the Year," in Circus Magazine (copyright © 1978 by Circus Enterprises Corporation), February 16, 1978, p. 24.