Gala Opening, Royal Festival Hall, London

Acoustics have much more clarity, but the real test is yet to come

So here we are at last. With four orchestras on stage and the auditorium packed with glitterati - not quite as many paying £500 for their seats as had been hoped - the Festival of Britain's showpiece venue is back on stream, after its fastidious £111m refit. A big day for London - as genuine as the opening of the Millennium Dome was false - and a moment of sweet nostalgia for those of us whose infant minds were blown by the sight of this Modernist apparition in 1951, with its message that the war was over, and imagination could take wing.

Last night, courtesy of two of our most cutting-edge composers, imagination took wing again. Just as Handel's "Hallelujah Chorus" opened the hall in 1951, so Julian Anderson's "Alleluia" - a Hallelujah Chorus for today - was now the first piece we heard. It focused on just one word, but with as many harmonies, textures, and rhythms as could be wrung from it: a tour de force which Vladimir Jurowski and the London Philharmonic plus the Philharmonic Choir turned into something rich and rare. The luminous thicket of sound with which the piece opened developed gracefully towards its climactic explosion of extemporised shouts.

Harrison Birtwistle's contribution was a rewrite of his 18-year-old funeral lament for the London Sinfonietta's director Michael Vyner: poignantly, some of the original musicians were playing the new version, "Cortege", today. If the first version had smouldering power, it's now more of a bonfire.

Both this and Charles Ives's The Unanswered Question brought us to the question of the night: had acoustician Larry Kierkegaard's labour produced the promised sonic glow? Had all those expensive tinkerings with the hall's interior cladding created a space which would no longer - in Sir Simon Rattle's famous phrase - sap the performers' will to live? This is an intensely subjective matter.

Nobody railed against the acoustic in the Sixties, and pianist Mitsuko Uchida relished its "clear and cool" sound. But with new auditoriums showing how intimate large-scale performances can be, we've become painfully aware of the South Bank's lack of reverberant warmth.

As Marin Alsop skilfully steered Ives's visionary work, with solo wind instruments singing out over a susurration of unseen strings, the hall really did seem to respond. It did so even more with Stravinsky's Firebird, whose finely calibrated colours came up bright and clear: the brass was incredibly vivid, the bass drum made you jump, the horn and bassoon solos in the Berceuse had irresistible warmth. The muted tone-clusters in Gyorgy Ligeti's Atmospheres found ample space to breathe; the solo voices in Beethoven's Ninth surged out as they should, and the massed choirs sounded glorious; the drummers in Ravel's Boléro beat up a storm. In a nutshell: the acoustic has much more clarity, and allows a vastly bigger sound, but there are still anomalies. For example, the piccolos now sound painfully bright.

Yet kaleidoscopic though this evening was, it represented only half the battle. The real acoustic test will come on Thursday, when Alfred Brendel plays his Steinway. Then we shall know.