Common almost has it right. Isaac Newton said, "If I have seen farther than others, it has been by standing on the shoulders of giants." On the cover of his fifth album, Electric Circus (MCA), the miniaturized heads of his ’80 collaborators — in life and in music — rest atop a pensive, too-serious Common, who’s bald-headed and sports a full beard. It’s a veritable who’s who of black bohemia, from rappers Dead Prez and Black Thought to R&B singers Jill Scott and Mary J. Blige to cultural icons Assata Shakur and Louis Farrakhan. These are the folks Common leans on for support, guidance, and wisdom. But the idea itself is a borrowed one. A Tribe Called Quest littered the cover of their 1993 album Midnight Marauders with the faces of dozens of their peers, and the art on Electric Circus is almost a direct homage. And more than any other group, it’s A Tribe Called Quest whom Common has always hoped to emulate. On "Come Close," the new disc’s first single, he plays Q-Tip to a near fault, and he’s aided by the Neptunes, who lace a beat so 1992 it practically comes with a "vintage" stamp. The warm organs and sparkling bells match the lethargic drums, and Mary J. Blige’s muted singing helps flesh out this nostalgic trip down rap’s memory lane.

But in the end the cover of Electric Circus and the tenor of "Come Close" are both misleading. In the years since he left Chicago for Brooklyn, Common has lost faith in conventional hip-hop as a path to righteousness, and who can blame him? There’s been precious little room in the rap mainstream for an artist whose primary appeal is earnestness. So though "Come Close" is a nice gesture in the direction of the type of hip-hop that Common would like to make, much of the rest of Electric Circus is an example of the kind of hip-hop he’s been forced to make. Sometimes it’s miraculous; sometimes it’s insufferable. But it’s almost never boring.

The best sonic trip here is "I Am Music," a jive-dance collaboration with Jill Scott and trumpeter Nicholas Payton. Scott chirps sweetly on the chorus, and Payton does his best Louis Armstrong. Bopping along at better than 100 beats per minute, it’s the best realization of a decade of attempts to fuse hip-hop with jazz. Common is just as comfortable on "I Got a Right Ta," another Neptunes production. Here his stretched-out delivery matches the texture and wonder of the Neptunes’ harmonica-accented crunky-tonk beat.

These fleeting moments in which Common is just as progressive as the beats are exhilarating, but they’re far too rare — what with changing outfits so often, he never gets comfortable in any one role. "New Wave," a collaboration with Laetitia Sadier of Stereolab, is meant to be some sort of goth-tronic art-funk excursion, but Common’s aimless rant seems out of place. When he’s alongside Sonny of P.O.D. on "Electric Wire Hustle Flower," his intrinsic congeniality prevents him from tapping into the kind of aggro attitude the track needs.

Worse still are the extended concept jams: if they never find a center, that’s largely because they never aim for one. "Jimi Was a Rock Star" groans on for more than eight minutes, shifting tones often but never amounting to much more than hollow dub. "Aquarius" is hot-buttered Afro-psychedelica with cameos by Bilal and Erykah Badu, but this song is merely an idea, a skeleton without flesh. The political humanism that’s been the foundation of Common’s best tracks doesn’t cohere this time around. And with lyrics that are less narrative-driven than those on his previous efforts, the musical eclecticism of Electric Circus never gets a chance to jell.

Last month, Common debuted material from Electric Circus in a pair of shows at the New York club S.O.B.’s. Both events were joyous affairs attended by a cadre of eager fans grateful for the return of their hero. Mos Def might have more charisma, and Talib Kweli might be more intelligent, but Common remains the most popular of the practicing bohemian MCs. He’s handsome and engaging, and his songs appeal to both women and men. He given life to some of Electric Circus’s more mundane material on stage. But the crowd gave him the biggest response when he rapped a few bars of Biggie Smalls and a few bars of the Wu-Tang Clan. We appreciate your excursions on our behalf, they seemed to be saying, but don’t lose sight of those upon whose shoulders you truly stand.