[With] the release of Physical Graffiti, Led Zeppelin's sixth album, the question [of what group is the world's best rock band] has actually become relevant. This two-record set, the product of almost two years' labor, is the band's Tommy, Beggar's Banquet and Sgt. Pepper rolled into one: Physical Graffiti is Led Zeppelin's bid for artistic respectability.

In a virtual recapitulation of the group's career, Physical Graffiti touches all the bases. There's a blues ("In My Time of Dying") and a cosmic-cum-heavy ballad ("In the Light"); there's an acoustic interlude ("Bron-Y-Aur") and lots of bludgeoning hard rock, still this band's forte ("Houses of the Holy," "The Wanton Song"); there are also hints of Bo Diddley ("Custard Pie"), Burt Bacharach ("Down by the Seaside") and Kool and the Gang ("Trampled under Foot"). If nothing else, Physical Graffiti is a tour de force.

The album's—and the band's—mainspring is Jimmy...