Rihanna, O2 Arena, London

In the boulevards outside the O2 Arena, an already half-forgotten Big Brother winner skips happily past me, trailing screaming girls in his wake. Inside, young girls in Rihanna T-shirts and tutus link arms, showing pop devotion's more appealing side. Both sights are more memorable than Rihanna's actual show, which celebrates the 10 weeks at No 1 for "Umbrella" with an overblown yet old-fashioned spectacle.

Rihanna turned 20 last month, and has already sold nine million copies of her three albums, helped by friends such as Jay-Z, Justin Timberlake and Sean Paul. But, watching her walk on in a black spandex fetish jacket, bustier, ultra-hot pants and stiletto boots, you have to wonder who has moulded her success. "Where my ladies at?" she asks, before joining her two similarly clad female dancers in wiggling their bottoms, as a prelude to "Break It Off". It's like watching the death of feminism to an R&B beat.

Worse for Rihanna, when she poses cocked against the mic stand for "Rehab" as if she's a torch singer, then draws on her West Indian roots for Bob Marley's "Is This Love", the skimpy leatherwear looks ludicrous. Whatever late-night rap channels may feel, Half-Dressed Dominatrix is not an all-purpose style for young female singers. It's also the exact look Madonna was courting mild controversy with circa 1992. When her dancers stretch and pose in slow motion as she slips off her jacket, it is a Hollywood "gentlemen's" club's idea of sexuality and transgression.

"Good Girl Gone Bad", dedicated "to all my bad girls out there", sets a similar lyrical template. "You better learn how to treat us right," she asserts, of a bad boy who's left her broken and boozing in a club. But she follows it up with "Hate That I Love You", which is nothing if not masochistic. The final irony in Rihanna's dominatrix look is that this slight Bajan girl, barely out of her teens, seems naturally pliant and nice. It is as if her lithe, dancer's body has been dressed by older, male hands, to suit their own fantasies. Amy Winehouse's wild, wilful self-destruction suddenly looks almost healthy.

Rihanna's two backing singers, meanwhile, wear more tasteful cocktail dresses, and carry the songs. Her rougher voice cuts across them almost randomly, and is only strong when buffed by effects. Look at the video screens, and you can admire Rihanna's looks, and diamond-encrusted mic. Look at the stage, and her real performance has no charisma, no defining persona. She could be a mannequin, or a hopeful rap video extra.

When Rihanna slips off for a costume change, we are taken still further back in time, to some awful Eighties Broadway dance "piece", incorporating bits of Tron, and Cabaret's pink boas and hats. Guitar solos from the usual expensive, hack band signify rock'n'roll, as Soft Cell's version of "Tainted Love" forms the undercarriage of "SOS".

Even when "Don't Stop the Music" stumbles on a genuinely driving, house cyber-beat, cages are wheeled on to clamber into athletically. "Shut Up and Drive" sees Formula 1 flags and pit-babe outfits. It seems amazing that the young crowd are sitting still for this misbegotten mess, until I realise that they have seen it on American television. From American Idol to Oscar night, Rihanna is offering the kind of tackiness that still passes as mainstream showbiz in the US; which, for many, pop is now reduced to.

She returns for the encore lounging on a zebra-striped chaise longue, and lets the crowd sing much of "Umbrella", an R&B power ballad as old-fashioned as everything else tonight. It's like punk, disco, and the 21st century never happened.