Black Star's Mos Def And Talib Kweli Are Black Star was one of last year's best albums, it's most remarkable quality being that it didn't just feature a new sound and a new style; it came with a moral philosophy. But while Kweli is the duo's secret weapon, kicking intricate and direct verses with purpose and urgency, Def has the star power. With his movie-star looks (he was an actor before delving into hip hop), charisma, and powerful delivery, Def is primed to become hip hop's next breakout star. But as impressive as his work with Black Star is, his first solo album, the provocatively titled Black On Both Sides, represents a giant leap in scope, ambition, and sonic variety. Like Lauryn Hill, Mos Def is a hip-hop artist so undeniably gifted that even the genre's detractors should pay at least grudging respect. Hill and Def pretty much embody the antithesis of everything people hate about rap: Think rappers only rap because they can't sing? They can do both. Think rappers aren't truly musicians because they don't play instruments? Def is a multi-instrumentalist as well as a rapper. Think rappers only talk about guns, sex, and violence? Def's lyrics here run the gamut from lyrical abstraction to social criticism to pop-culture rhapsodizing. Black On Both Sides is one of the most focused and powerful debut albums hip hop has seen in years, embodying everything from irresistible pop-rap ("Ms. Fatbooty") to a fierce critique of white culture's appropriation of black music and culture that moves steadily from laid-back funk to hopped-up pop-punk ("Rock 'n' Roll"), to a Q-Tip collaboration that builds on A Tribe Called Quest's "Sucka Nigga" ("Mr. Nigga"). Like most artists who commit themselves to saying provocative things, Def occasionally slips into questionable territory—his defense of O.J Simpson is no more convincing than Chuck D's—and just because Def can sing doesn't mean he always should. But Black On Both Sides is a landmark debut that could, and should, have a long-lasting effect on its genre.