Review: Live 8

Virtually every act at Live 8 makes some reference to the concert's capacity to change the world. Certainly, the world of rock and pop seems to capsize for its duration. The sheer overload of artists and celebrities is disorientating enough - as they scuttle on and off stage, it's like trying to watch a rock festival with your finger permanently stuck on the fast-forward button - but in addition, your expectations keep being confounded in the most unlikely ways. The most cutting-edge stuff on offer keeps falling a bit flat.

Pete Doherty's guest appearance with Elton John is most notable for the look of mild, almost paternal panic that crosses Sir Elton's face as the errant ex-Libertine hoves unsteadily into view, a cigarette lighter in his mouth.

Alt-rock stars Razorlight kick over mic stands, take their tops off, bend iron bars with their teeth, etc, in the hope of making an impression. It might have worked if they hadn't been followed not just by Madonna, but Madonna on top form, hand in hand with a former victim of the Ethiopian famine, loudly berating the assembled journalists and VIPs in the "golden circle" in front of the stage. Within seconds of Like a Prayer starting, you forget Razorlight were ever on stage.

For all the fuss about the lack of black faces on Live 8's bill, rapper Snoop Dogg somehow contrives to seem incredibly inappropriate. He never mentions the concert's aims, preferring instead to raise the watching world's awareness of Snoop Dogg. "Wave your motherfucking hands in the air," he yells. "Wave the motherfuckers like you just don't care." Given that caring is rather the point of Live 8, this suggestion seems unsuitable at best.

Meanwhile, things that you would expect to seem overblown and mawkish end up poignant, powerful and impossibly moving: white doves being released into the air during U2's set, Annie Lennox performing a solo piano rendition of Why? in front of footage of African children stricken with Aids. Shown dozens of times in the past 20 years, the old Live Aid film of the Ethiopian famine set to Drive by the Cars should theoretically have had its impact dulled by familiarity. Instead, it stuns Hyde Park into silence.

Dido, of all people, packs an emotional punch, duetting with the Senegalese vocalist Youssou N'Dour on Seven Seconds. Bob Geldof apologises in advance for singing, but whether out of indulgence on the part of the audience or simply because it's a good song, I Don't Like Mondays goes down a storm.

The appearance of Sting causes the more cynical journalists to hasten from the backstage area in the hope of a catching a daft quote along the lines of the one he made at last year's Mojo awards, about how the Middle East crisis could have been resolved if only the warring factions had paid attention to the lyrics of his song Desert Rose. They are out of luck: he keeps his trap shut between songs and instead changes the lyrics of Every Breath You Take into a glowering, powerful indictment of the G8 leaders, who slope past on the onstage video screens.

Aside from the absence of Status Quo, it is one of the most noticeable differences between the Live 8 concert and its predecessor: technology has advanced in the past 20 years, so that the giant screen's frequent visuals end up making as much impact on the audience as the music itself.

The guaranteed success of seasoned practitioners U2 and REM restores some sense of order to brains overheated by the concept of enjoying Dido, but there's a whiff of missed opportunity about the latest graduates to the rock aristocracy, Coldplay.

They start out well with In My Place, which Chris Martin interpolates with a snatch of Rockin' All Over the World, but then go oddly off-piste. Martin introduces Richard Ashcroft singing Bittersweet Symphony as "the best song ever written sung by the best singer in the world", which even the most devoted fan of Ashcroft's former band the Verve might consider gilding the lily a bit.

Then they break a cardinal Live 8 rule, ending their set not with a big hit, but a downbeat track off their new album (the Scissor Sisters do something similar later, but remarkably get away with it as the new song is blessed with a chorus that burrows into your brain within seconds). Martin leaves the stage with an announcement about the importance of the film that's about to follow. The video screens immediately show jowly old Duran Duran at the Rome concert. Either there's been a technical error, or the gravity of the occasion has sent Martin bonkers.

For the first half of the show, the videos between artists give the Hyde Park audience ample opportunity to reflect on those in faraway lands less fortunate than themselves. They could, for example, be in Canada, watching a bloke who looks like the 70s northern comic Norman Collier huffing through a harmonica and singing about life being a highway.

As evening closes in, the show begins to overrun. Sets seem to be cut short. Razorlight get three songs, Snow Patrol get two, but the Killers, who have more anthemic hits to their name than Razorlight and Snow Patrol put together, only get one, a fantastic All the Things I've Done.

Whether this is really down to late running, or worries about the effect their creepy lead singer Brandon Flowers might have on the global viewing public, is open to question. Dead-eyed and waxily handsome, he makes a speech about helping our brothers and sisters in Africa. It sounds chilling, like Ming the Merciless ordering the immediate destruction of Earth. The Killers' set seems so truncated that you begin to worry what's going to happen next.

Fears that subsequent artists might be forced to simply sprint across the stage waving are assuaged by Joss Stone, whose appearance seems to go on for weeks. Mariah Carey, meanwhile, seems to be on for months, like a one-woman mission to bore the G8 leaders into submission.

After her, you suspect that Robbie Williams could come on, read the long-range weather forecast and still be greeted like Caesar entering Rome. Instead, he does his all-guns-blazing routine, involving a cover of Queen's We Will Rock You, a kiss for a girl in the front row and a finale of Angels: the well-worn cliche about his great showmanship is well-worn only because it is true.

From then on, it's plain sailing. The Who's Won't Get Fooled Again still fizzes with a righteous anger. The much-touted reunion of Pink Floyd exceeds expectations. They look like senior partners in a firm of chartered accountants, but 24 years after they last shared a stage, they sound fantastic. Often icy, aloof and didactic on record, their music unexpectedly takes on a warmth and humanity, fuelled both by the thaw in relations and the emotions of the day.

Famed as a model of gloomy severity, the bassist, Roger Waters, touchingly dedicates Wish You Were Here to the band's doomed founder Syd Barrett. They play a glorious version of The Wall's Comfortably Numb, then embrace, albeit briefly and tentatively.

Finally, Paul McCartney pulls out the last surprises of the day - an unannounced appearance by George Michael for Drive My Car, then a rampaging take on an unlikely song, The Beatles' ominous 1968 track Helter Skelter.

As the assembled musicians troop on for an extended coda, Hey Jude, even the most cynical observer would be forced to admit that, even judged on music alone, Live 8 has been a remarkable day.

· Alexis Petridis is the Guardian's pop and rock critic