The White Stripes, Royal Court Theatre, Liverpool

Oh, hyperbole. Oh, adulation. Jack and Meg White return to these shores in a blaze of glory. Their fourth LP, Elephant, is widely regarded as the finest album of 2003, and the vacuous phrase "saviours of rock" rings in the duo's ears.

The White Stripes are not the world's greatest rock'n'roll band - rock'n'roll usually sounds better with bass. They're something else. For a start, they're not a band. True to their resolute minimalism, only the two of them appear on stage - Jack thrashing the guitars and keyboards, and Meg banging the drums with determination and occasional girly flourishes. Of course, you do get thrilling rock moments, from the mighty "7 Nation Army" to the punk tantrum of "Black Math", with which the pair hit the ground running tonight. Songs such as "Hotel Yorba" sound as though they have always existed and all Jack has to do is pluck them from the ether of pop genius.

"Hotel Yorba" provides one of several moments when The White Stripes are simply electrifying. As Jack slithers about the stage like a man possessed, the energy coming from just these two people is astounding. In this context, his howling rendition of Dolly Parton's "Jolene" is heart-rending. And the boy sure as hell can play guitar.

But don't let's go mad. We're talking scrappy, rough-edged, abrasive punk most of the time. It's simple and it wears its influences - blues, but also grunge - on its sleeve. There are incoherent periods. There are lulls. "I Want to Be the Boy to Warm Your Mother's Heart", with Jack trying to play keyboards and guitar at the same time, is not as good as on record, and in general the duo rely too heavily on one constant guitar sound. If the music were all The White Stripes had, they'd still be the best of the current crop of American retro-garage acts but nothing beyond.

In fact, they're much more fascinating. Their shows could be analysed like performance-art pieces, centring on the stripped-down concept and the enigmatic relationship between Jack and Meg (they're brother and sister, and they got married... maybe?). It's the way he creeps around her, playing his Pink Panther riff as she sings "In the Cold, Cold Night", or the way she sings it... Taken at face value, the gender politics in the duo don't seem very 2004.

But Jack's lyrics are written for some forgotten era when romance was at once more innocent and more regulated, when it was important to "be a gentleman" and to impress your true love's mum. For a saviour of rock, he seems strangely attached to the very values rock'n'roll tore down 50 years ago. Yet sentiments that might seem nostalgic or even reactionary somehow become moving in the hands of the Stripes.

Because really it's about something more abstract and more universal: the notion of beauty fighting to shine through constraint. The restrictions The White Stripes place on themselves, from the equipment they use to the clothes they wear, are all designed to energise their music. Their romanticising of old-fashioned values works on the same principle. Elephant is dedicated to "the death of the sweetheart", the one you had to pine in agony for before you could have. That ties in with Jack's love of both the De Stijl aesthetic and the blues. (Blues and country covers abound tonight.) Roots music and modernist art, worlds apart yet from the same era, use restricted forms. There is a wonderful coherence to the whole White Stripes project.

What sets them apart from the rest is that they have turned a concept into something that grabs you in the guts, sends you pogoing three feet into the air and then makes you cry. They've made the idea work: The White Stripes believe heart and soul in every note they play, as no one at tonight's show could doubt for a second.