Of course, they could also be numbingly stupid, boring, or worse. Live performances often bore interminable and unfunny resemblances to Spinal Tap, and particularly later in their career they were prone to fatal levels of bloated pretentiousness. And then there are the disconcerting racial issues, the fact that Zeppelin treated much of their blues-derived source material either cavalierly or with a caricaturing tendency that verged on parody. Sometimes bad Zeppelin and good Zeppelin even sit side-by-side in the same song, such as "Bring It On Home": two and a half minutes of jaw-dropping power sandwiched between and intro and outro of minstrel-ish hogwash.
Many of these more unseemly elements coalesced around Plant himself. Plant's vocal idol as a young man was Ray Charles, and certainly among young Britons he wasn't the only one. Unlike Joe Cocker or Steve Winwood, though, Plant never seemed entirely comfortable relinquishing the squarer sides of his Englishness, which clung to him like so many of Tolkein's ringwraiths he was fond of crooning about. Here was a singer who'd punctuate Robert Johnson's lyric "squeeze my lemon / till the juice runs down my leg" with an "I wonder do you know what I'm talkin' 'bout?"—no, Mr. Plant; please do explain.
Led Zeppelin's blues cosmology was painfully literalist, all squeezed lemons, backdoor men and every-inch-of-my-love's, an inclination that might go a long way towards explaining some of the band's own lyrical deficiencies. "Let the music be your master / will you heed the master's call?" from "Houses of the Holy" might be the single worst lyric ever written; every line of "Stairway to Heaven" is in an endless tie for second.
Plant's best vocal performances were always ones that forced him toward understatement, and in general Led Zeppelin's quieter music is the most underrated part of its catalogue: "Tangerine," "That's The Way," and "Hey Hey What Can I Do," perhaps the best song the band ever wrote. A large part of this is due to Jimmy Page's unsurpassed talents as an acoustic guitarist, but part is also due to Plant's voice, one of the prettiest in rock when he allowed it to be.
Band of Joy finds him working entirely in this vein and its best performances, such as the rendition of Townes Van Zandt's "Harm's Swift Way," are closer to the spirit of Ray Charles than anything Plant has ever sung. Nowhere is this more evident than in his carefully loving version of the gospel classic "Satan Your Kingdom Must Come Down," a song it's nearly impossible to imagine Led Zeppelin approaching subtly (see their eleven-minute version of "In My Time of Dying" for an idea).
In this sense, what's most interesting about Robert Plant's second act isn't what it tells us about the continuing popularity of roots music, or even the state of Plant's career, but rather what it tells us about Led Zeppelin, one of the most influential and continually confounding bands in all of rock and roll. The critic Robert Christgau once referred to Led Zeppelin as "genius dumb," a funny and memorable appellation that manages to be both spot-on and not entirely fair. Led Zeppelin wasn't dumb, they just weren't quite as smart as they thought they were. By abandoning dubious fantasy and pretentious hysteria and learning to embrace his music on its own terms, Plant's doing some of the finest work of his career. Heed the master's call, indeed.