Vienna PO / Gergiev, Barbican, London <!-- none onestar twostar threestar fivestar -->

Valery Gergiev may be the hottest conducting property around these days, but, for better or worse, he's still a "fasten your seatbelt and hang on" man. The Barbican, beginning its 2006/7 Great Performers programme, went for more M&S - Mozart and Shostakovich - in a concert where square pegs in round holes kept coming to mind.

The Vienna Philharmonic Orchestra is known for having no women players (although now there are a sprinkling) and no music director. The players like to choose their conductors and tend to like those best that leave the orchestra well alone. The orchestra has sat on its laurels for a very long time - its string sheen, its prowess in the great classics, accounting for its position. But along comes Gergiev and the walls appear to tremble.

Scarcely pausing for breath, Gergiev plunged into the (distinctly fast) slow introduction to Mozart's Linz Symphony at such a pace that even the orchestra seemed taken aback. And then the following Allegro appeared distinctly slow, heavy bows clinging to strings in anything but a "spiritoso" fashion (as Mozart advises). This was Mozart at his grimmest - it's not a grim symphony, but Gergiev seemed determined to give it a workover.

Where was the silky sound, the plummy warmth, the tenderness? Even the elegant, refined Menuet and Trio were driven like a cart, no space allowed for the excellent oboe and bassoon solos. Even if the string section is awesome at speed in its ensemble passage work, what's the point if phrase endings are so snatched? Here was an orchestra not sounding like itself. But then came Shostakovich.

Gergiev is trundling through all of Shostakovich's symphonies in this anniversary year - it seems amazing that there are still six (out of 15) to go - with various orchestras. And it becomes clear that he attempts to mould all of these orchestras in a similar fashion. Some respond well - the LSO, for instance. As for the VPO, they rose to the occasion spectacularly in the Fifth, but seemed jolted and shocked in the rawness, passion and sheer volume of their playing. The horns in Shostakovich's grotesque Menuet bayed for blood, the divided strings in the Largo seeped warmth and pity.

Gergiev's demands leave everyone on edge - orchestra and audience. This music is deadly.