Blackalicious' Nia shoulders a considerable burden. The duo of Chief Xcel and Gift of Gab carry expectations of underground fans hoping for a sea change in rap music's direction. As part of the Quannum (formerly Solesides) family, the Bay Area's Blackalicious, along with DJ Shadow and Latyrx, have manned the vanguard of the West Coast's indie revolution. From anchoring hip-hop's moral center, to breaking new ground in musical and lyrical innovation, to straight entertaining the crowd, Nia strives to be a truly definitive album. Is it any surprise that the album's Swahili title translates into "purpose"?

At times, the album's myriad directions feel hydralike, but Chief Xcel and Gift of Gab provide moments of brilliance that lend coherence. For Xcel, sometimes eclipsed by the attention given his labelmate DJ Shadow, this work is his first major exhibition of beat artistry, and he takes full advantage. From the Afro-centric riddims on "Smithzonian Institute of Rhymes," (RealAudio excerpt) through the jangling piano melody of "A 2 G" (RealAudio excerpt), to the nasty, throbbing bass loop on "Ego Trip," Chief Xcel finally shows off a complete fabric of tracks after tempting us with mere swatches in the past. Likewise, Gift of Gab lives up to his name through streaming flows of rhymes on songs such as "Trouble" and "The Fabulous Ones," which race the rhythm in speed and density. More than just a bare bones braggadocio MC, though, Gab also fashions morality plays on "Shadow Days" and "Making Progress," while exploring his soulful side on "As the World Turns."

Still, the album's lofty ambitions lead to some inconsistencies. With so many threads to follow on this 18-track album, it's easy to feel lost. Also, not every concept works: For (worst case) example, Gab's attempt to draft a rap noir vignette on the six-minute marathon "Cliff Hanger" ends up being far less interesting than DJ Shadow's techno-meets-horrorcore track of drum & bass blasts and dub drifts. And, ironically, for all its iconoclastic intentions, Nia's more conventional songs ("A 2 G," "Trouble") are key to keeping the album grounded in accessibility.

The album's overall success ultimately is the result of the remarkable chemistry between Gab's sinuous syllabics and Chief Xcel's soul-engineered beats. On "If I May," (RealAudio excerpt) Xcel kicks off the track with shimmering cymbals and an acoustic guitar loop, then in glides Gab, proclaiming, "Here we go again/ Slip into my conscience/ Come along and take in/ A story about a battle/ In this corner Satan." He hardly seems to pause for a breath as he continues to spill his words — and you'll probably be left breathless, too, until the song ends.