I Have often found something a little eerie in the Kirov's corps de ballet, with its dozens upon dozens of identikit girls whose admiral lengths of neck, slope of shoulder and torso-to-leg proportions suggest some secret pre-Gorbachev programme of genetic engineering. But in both the ballets the company showed last week - a refreshingly straightforward production of Swan Lake and sublime Giselle - one ceased to wonder at the uniformity, and marvelled instead at the diamond security of technique that enables some 40-odd slips-of-things to dance as one. As swans they present a mirrored wall of perfectly angled limbs. As the spectral Wilis - the ghosts of jilted maidens who force their deceivers to dance themselves to death - they produce the deliciously extended frisson that first ensured that Giselle, uniquely among romantic ballets, would remain in the company's repertoire for 150 years.

I once asked an ex-prima ballerina the proper name for those hopping arabesques that the corps so memorably perform in both Swan Lake and Giselle (and which Morecambe and Wise so delighted in mimicking lumpenly.) "We call them the Big Hops," she said unhelpfully. I had always thought them awkward, ungracious steps, invented merely as a technical hurdle to be overcome as best a dancer might. But the Kirov makes all clear. With the lifted leg floating high and apparently motionless behind, one arm yearning forward to balance the shape, the girls' slender, gauze-clad forms advance like a drift of enveloping mist; a vision of whiteness conveyed on invisible wheels.

If the well of superlatives is in danger of running dry for the company dancing, words utterly fail for the Kirov's newest discovery, Svetlana Zakharova. At 18 years old and only just, she well and truly falls into the category of the Russians' fabled baby ballerinas. Yet her artistry is already astounding. When she picks up the hem of her skirt and hops prettily on one toe across the stage, her lifted foot tracing dainty circles as she goes, she is not just performing one of the 19th century's most popular stunts, but establishing further a most convincing and affecting portrayal of purity.

The snag of this ballet is that all the best spectacle comes in the second half and much of the first is taken up with formal mime. Our Royal Ballet's production dilutes this aspect by playing the action naturalistically. The Kirov, by contrast, raises the original gestural language to such a rarefied pitch that it becomes a thing of beauty in itself. Resisting the temptation to "fill in" mimed conversations with stage business, these characters simply stand and deliver - with the most expressive economy - and wait for the reply. It's as clear as if a speech bubble were hanging over them. And it's quite the reverse of dull.

Igor Zelensky's Albrecht is an object lesson in how to fill a stage by doing nothing at all. It can't be nothing, of course, because all eyes are drawn to him constantly. But he is blessed with that rare ability to express joy, tender concern, even abject despair without noticeably rearranging his features. The extraordinary power and lyricism of his dancing, in a ballet that offers limited opportunity for showing it, comes almost as icing on the cake. Seeing his Siegfried in the same week has quite possibly spoilt me for heroes for good. It's all downhill from now on.

The Kirov's staging of Swan Lake is uncluttered to the point of plainness, save for the tiresome presence of a jester - Vyacheslav Samodurov in the performance I saw, who redeemed himself with the cleanest and springiest of scissor jumps. We are led to believe that this is the one true traditional Swan Lake. The Royal Ballet makes a claim to the same, yet there are many differences of detail. Here I missed, for example, the enfolding arms motif in Odet's first pas de deux which has simply been wiped from the text. And I regretted the ludicrous ending, an intervention of the Soviet years designed to send the proles home happy. But for the most part this grandly formal treatment lets the choreography speak for itself.

The keen presence in the audience of two of the Kirov's most famous former Odettes gave substance to the rumour that the one we were seeing - Yuliana Lopatkina - is strongly fancied in Russia today. Owner of a modishly string- bean physique, her languorous control in the white act is remarkable (at times the music slowed almost to a stop). Conversely, her Odile is the speediest, bitchiest, hungriest-looking creature a tall prince could fall prey to. Twice she slowed midway through a lightning pirouette to lick her lips.

Feelings were more mixed at Monday's gala which lowered the curtain on the Royal Opera House. There was regret that we'll have to live without its inimitable glamour for two years. There was joy at the promise of more legroom and lots more cheap seats when it reopens (the logistics of which are rather puzzling. There was dismay that, with artists of the calibre we were seeing assembled on one glorious night, the Royal Ballet still seems unable to offer them the sort of artistic challenges that will keep them in our sight. The re-hashed fare the company has chosen for the next two years must make their hearts sink.

In an evening of snippets and chunks, the ballet (an art of the scintillating moment) fared better than the opera, which suffered from lack of context. Most thrilling was Mukhamedov, flinging his meaty frame into the airborne huntsman poses of Diana and Actaeon. Most moving was, yet again, Igor Zalensky, a palpitating Romeo to Darcey Bussell's Juliet. Theirs is a star-crossed part- nership that must be allowed to develop.

The final item may have mystified some. With the entire personnel of the two Royal companies on stage, Darcey Bussell's Lilac Fairy (from Sleeping Beauty) bourree'd to left and right, wafting her magic spell, first to dismiss scenery (revealing an ugly wasteland behind), then to put the building to sleep. But not, we trust, for 100 years.

The Kirov's Swan Lake: Coliseum, WC2, (0171 632 8300), Mon to Thurs.