Meltdown: London Sinfonietta/ Alsop, Royal Festival Hall, London

Even before it started, David Bowie's curating of the 10th Meltdown festival was getting a bad press: too familiar this, too obscure that. So it was fitting to start by reviving two Nineties works that had an equally bad press almost before they were played. Philip Glass based his first and fourth symphonies on themes from the Low and Heroes albums on which Bowie and Brian Eno collaborated in the late Seventies. The idea sounded like returning a compliment, since the albums borrowed classical techniques including the minimalist styles that Glass and others used in their early days. It naturally upset two groups of people, the Bowie fans who thought Glass had dried up all the rock spirit, and the classical critics who couldn't stand anything Glass did.

Approaching this music as a Glass-watcher makes life a whole lot easier. For a start, Low sounds just like "normal" Glass. He has said that he wrote it to give a boost to the experimental record label that he was helping to run at the time, and that audience is very much the constituency he is addressing. Still, to hear it live now gives it a new context, since it turned out to be the start of a substantial symphonic line.

It's a very confident first symphony, not surprisingly since Glass had plenty of experience in extended orchestral writing. The music is very much his own at symphonic length. Only the middle movement, "Some Are", is a straightforward scherzo, complete with meltingly lyrical trio section, Schubert-style. The first and last grow in their own way, with blocks of characteristic Glass material alternating, displacing one another and proliferating. Unless you knew the Bowie allusions, you wouldn't notice. Instead, there is some notably fresh and light orchestration, a long slow build in the first movement to a single full-band statement at the end, and a sombre finale with more relaxed interludes, this last rather glum in impact but personable enough.

Heroes, a follow-up based on a follow-up, is more of a dance symphony. The six movements are more concise, varied and colourful, and the tunes often sound like quotes, dressed up as classical composers like to do when they are going to write a set of variations. Not that that's what happens: Glass uses direct, clear-cut forms, usually with a separate middle section, and the music is more about statement than development, at least until the bouncy "V2 Schneider" at the end. The result is like a sequence of short tone poems, at its strongest in the upbeat "Abdulmajid", which flirts with exoticism and never quite succumbs, the exploratory "Sense of Doubt", and the stark "Neukoln".

Lively and focused performances by an enlarged London Sinfonietta, conducted by Marin Alsop, drew the eclectic audience from a somewhat thoughtful initial response to a mood of some enthusiasm. Alsop, who seems to have joined the handful of trusted Glass interpreters, has now conducted all of his orchestral symphonies in London in six months. Time for her to have her head with the two vocal-orchestral works that followed them. One of Britain's choruses should have picked up the epic Symphony No 5 by now, and while No 6 is brand new, as soon as word gets around about its intense soprano setting of Allen Ginsberg's anti-nuclear "Plutonian Ode", by some way Glass's most powerful concert work, the demand will be there.

Meltdown continues at the South Bank Centre, London to 29 June (020-7960 4242 & www.sbc.org.uk)