R&B

Keri Hilson, "In a Perfect World" (Interscope)

Two years ago, Hilson was the sweet-voiced singer on "The Way I Are," the bizarre song that turned hip-hop producer Timbaland into a pop star in his own right. The unfortunate pairing is reprised on "Return the Favor," which appears on Hilson's debut album and encapsulates the record's shortcomings.

Hilson is clobbered on all sides by ornate production -- largely by Timbaland and Polow Da Don -- throughout this album, which favors texture and rhythm over melody or feeling. Sometimes, as on the slinky single "Turnin' Me On" (featuring Lil Wayne), the busyness coheres, with Hilson neatly gliding among the song's many layers. And she may need the crutch; she is a careful, slight singer.

But she's often inventive, approaching the beat from odd angles and picking unexpected moments for rhyme. Knowing how best to frame other singers (she's written hits for Usher and Omarion) hasn't helped Hilson make better decisions for herself. Her sharpest moments are also the least frequent ones here: the uncluttered ones. The excellent "Slow Dance" sounds like a mid-1980s Prince ballad, sparkly and psychedelic, and the album's high point, "Alienated," is an alluring cloud-covered plea to an ex in which Hilson alternates between singing and a sort of whispered rap.

JON CARAMANICA, NEW YORK TIMES

POP/ROCK

Mastodon, "Crack the Skye" (Reprise)

Since forming in Atlanta a decade ago, Mastodon has earned its place at the forefront of progressive metal with a mix of headiness and brawn. The band's fourth CD completes a cycle tied to the elements: fire, water, earth and now air. Fantastic in every sense, the album is also girded with hard-fought musical and emotional maturity. It isn't an impregnable fortress. Its energies are sprawling, reaching not just for impact but also for a kind of release.

Sober reflection had something to do with it. Brent Hinds, the band's lead guitarist, wrote much of this music shortly after a serious head injury. Mastodon also mines more exotic sources of dread: assassination plots in czarist Russia, cosmic wormholes, skulls spilling human blood. Exploring air as a theme, the band wheels through "vapor space," grappling with "the space-time paradigm." At times the language falls more in line with prog-rock than metal. So does the music, often forsaking blunt-force riffs for streaming convolutions, complete with stratospheric solos. Mastodon performs April 29 at the Fine Line.

NATE CHINEN, NEW YORK TIMES