Rotterdam PO / Gergiev, Royal Festival Hall London

The South Bank's Classic International series claims to present "The World's Finest Orchestras". Since it includes only visitors, you'd think the London orchestras would have ganged up and got it renamed by now. No one minds the Vienna Philharmonic being dubbed "finest", or Seiji Ozawa's Saito Kinen Orchestra, which played last month. But the Rotterdam Philharmonic?

The South Bank's Classic International series claims to present "The World's Finest Orchestras". Since it includes only visitors, you'd think the London orchestras would have ganged up and got it renamed by now. No one minds the Vienna Philharmonic being dubbed "finest", or Seiji Ozawa's Saito Kinen Orchestra, which played last month. But the Rotterdam Philharmonic?

That's to reckon without the Valery Gergiev effect. He has been music director there for nearly a decade, and the result is one of those must-hear partnerships that crop up a couple of times in a generation, in which a previously less-than-finest band manage to play out of their skins nearly all the time. Oslo and Jansons, and Birmingham and Rattle were famous examples. Surprisingly, the Rotterdam Phil's London appearance was only a hottish ticket, despite bringing the rare chance, in a concert, of hearing the whole of a favourite ballet, Prokofiev's Romeo and Juliet. This meant that even if the hall wasn't packed, the platform certainly was, with two harps, a piano, and enough kit for six percussionists pushing the horns and trumpets into corners - and that was before the 14 extra brass arrived for Act II.

Though the complete Romeo makes for a long evening, it is an experience far beyond the usual excerpts. Cross-references, continuity and cumulative power come into play, as do character and colour. Gergiev's long-range plan, which fully paid off during the final half-hour or so, let the music unfold in its own time rather than playing up local detail. You emerged thinking first, "what a great score", and only then, "that was some performance".

The sound of the orchestra involved playing out, balancing the volume upwards rather than fining down the tone, rooting it in massive but easily moving bass-lines, and letting Prokofiev's rhythms support the singing melodies where many conductors make them staccato and mechanical. All this produced some very loud, sustained climaxes. The impact was galvanising, but you could still hear plenty of detail, though the policy brought diminishing returns, since light and shade didn't come into it - this music can be shaped, and its harmonies given greater impact, if it isn't flat out all the way. But unrelenting assaults by trombone and tuba certainly became part of the grand scheme, even if touches of delicacy - a shudder of violins here, a glissando of violas there - fared better from moment to moment.

What counted for most, though, was the sustained concentration that led, with a sense of inevitability, towards the long wind-downs: the love scene, the feigned death of Juliet, and the final stages of the tragedy. Gergiev could let the music expand and dissolve in a way that isn't possible when it has to be danced, and the players seemed as single-minded as chamber musicians in real, shared music-making.