Subtlety not being part of Christina Aguilera's vocabulary, she trades the retro-swing of Back to Basics for the future-pop of Bionic, receiving assists from a roster that reads like a who's who of progressive pop: M.I.A., Le Tigre, Peaches, and John Hill and Switch, known for their work with Santogold. But like the half-cyborg/half-diva illustration of the cover, this revamp is only partial. Aguilera hedges her bets by adding a ballad from old friend Linda Perry, gets Tricky Stewart to produce a trio of cuts, and drafts Polow da Don and Focus to produce some heavy and slow R&B, letting enough air into the machines to reassure hesitant fans that she hasn't abandoned her roots. All this hesitancy means that for as many risks as it takes, Bionic doesn't feel daring.