SOME YEARS BACK, Mariah Carey did a “Fantasy” dance on a Brooklyn boardwalk with an unhinged, erratic rapper known to the world as Ol’ Dirty Bastard. Decked out in cut-off denim shorts and a tightly strapped T-shirt, Mariah was evolving from pained balladeer to playful pixie, bursting out for all the world to see.

Mariah Carey

Rainbow (Columbia)

On her earlier albums, Mariah’s nods to the dance floor always seemed awkward, as if somehow her prodigious voice was too formal for anything but a love song. But the ODB moment was a telling one. It may have been a calculated marketing move, injecting Mariah with a healthy dose of hip-hop credibility, but more importantly it signaled an expansion of Mariah’s comfort zone. Until that point, her music had been the product of extensive vocal training and an early, confining marriage to Sony president Tommy Mottola. Her balladry—”Vision Of Love,” “Love Takes Time,” “Hero,” and so on—was beyond reproach, not to mention crucial to her public identity. Cavorting around with the Wu-Tang renegade gave her a dash of spice (the intrigue only enhanced by the reports that she herself had requested the pairing) and, just maybe, a taste of what else the world had to offer.

Since the “Fantasy” episode, hip-hop has slowly crept its way into Carey’s repertoire, often awkwardly; her fluency may be minimal, but dilettantism will get you everywhere in contemporary pop. Both Mobb Deep (via sample) and Bone Thugs-N-Harmony (via collaboration) made inexplicable appearances on her last album, Butterfly.

On Rainbow, her seventh album this decade, the genre-dropping only gets more gratuitous. Last time around she claimed to be stuck off the realness. This time she’s just stuck.

Most emblematic of her difficulties is “Did I Do That,” an I-got-over tale unremarkable in content and delivery. To give it edge, though, Mariah loops the chorus from the No Limit anthem “It Ain’t My Fault” and makes it her own. Mystikal’s gruff gutturals, though, are utterly bereft of context; gone are the abrupt, clunky keys that marked the original, replaced by a too-slick synthesizer that is merely a pale cousin of the original.

Hollow sampling permeates this album, whether it’s the vague Tupac bite on the Usher duet “How Much,” the whiny, tinny faux G-funk of “Crybaby,” or the third-rate Timbaland-like syncopations of “Thank God I Found You” (produced by old-tymers Jimmy Jam and Terry Lewis, who tried the same bite on Janet Jackson’s last record to even lesser effect).

Even her ballads, long the true measure of her talent, seem hollow and unconvincing this time around. Gone are the fluid collaborations with songwriter Walter Afanasieff that have defined her career to date. Instead, she sings listlessly—no glissandos here—over what can only be termed knock-off tracks: “Petals” has hints of Seal’s “Kiss From a Rose” while “After Tonight” has Toni Braxton’s “Unbreak My Heart” inscribed in blood, if not royalties. Her indolence is most glaring on her version of Phil Collins’ “Against All Odds.” Her temperance on the cover is admirable, but no ballad is better suited for vocal and emotional histrionics—qualities Mariah once had in bundles but now seem willfully thinned.

It’s all laurel-resting of the worst kind, but not wholly unjustified in today’s youth-driven pop market. Wailing about broken hearts doesn’t cut it while teenage girls are busy finding love with Nick, Justin, Kevin, or one of the other Spice Boys. If they’d been listening to Mariah for years, though, all those groupies-in-training would know their idolatry is just a sweet, sweet fantasy, baby. But not as much so as Mariah’s pretension to urban cool. Dreamlover, come rescue her.