So much of Madonna's mastery and mystique is predicated on being at the forefront of emerging musical styles while pushing the envelope of social discourse.

Though she's long since ceased to be a cultural lightning rod (Britney kiss excepted), Madonna has still managed a few savvy sonic reinventions over an uneven past decade, taking techno (and yoga culture) to the masses on 1998's "Ray of Light" and later enlisting ultra-trendy producer Stuart Price for 2005's "Confessions on a Dance Floor."

Rather than help shepherd some underground genius into the mainstream light, however, Madonna has decided this time to draw from two of Billboard's deepest wells: Timbaland and Pharrell Williams. Were it 1998, such a move would fit the icon's pattern of riding the crest of pop's regenerative wave. But in 2008, she's merely queuing up behind Nelly Furtado, Justin Timberlake and Gwen Stefani.

In fact, there's good reason to suspect Williams and Timbo of being on the downswing of their own respective crafts, at a time when Madonna herself is increasingly reliant on sympathetic collaborators. The resulting album, "Hard Candy," makes a predictable mess of her lazy assemblage of star power and inescapable artistic baggage.

Timberlake and Furtado are comparatively unencumbered by their own histories, but the simple fact of Madonna making a "return to roots" dance-driven record is far too enormous for these uninspired tunes to surmount. The catty "She's Not Me" offers genuine levity, but most of the rest is weighed down by quasi-spiritual dance-floor edicts and stridently non-titillating sex talk.

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