Foo Fighters, Wembley Stadium, London

The Foo Fighters are one of the biggest rock bands in the world now, and I still struggle to see why. This first headlining gig at Wembley, and last album Echoes, Silence, Patience & Grace's debut in the UK charts at No 1, confirm their conquest here. But it has been a traceless rise, leaving few truly memorable songs or moments. All that lingers, as with tonight's show, is the fiercely grinning good humour and heart of Dave Grohl. The cliché that he is the nicest man in rock seems true, an honourable thing after his last band Nirvana's end. But musically, that means nothing.

Tonight's support band, Supergrass, Britpop heroes in the mid-Nineties wake of grunge's post-Cobain collapse, suggest Foo Fighters' missing ingredients. Hits including "Richard III", "Moving", "Caught by the Fuzz", "Pumping On Your Stereo" and the rarely played "Alright" combine careless adolescent fizz, dumb rock and melancholy pop, tackled here with stadium volume and pretty harmonies. Their hits' distinct, nagging melodies, the hooks that keep you hanging on, are what is missing later: the Foos' Achilles heel.

At least you can't fault Grohl for effort. When the gothic black cage around the stage is lifted, he runs down a walkway the length of the stadium, hollering throat-shredding exhortations, getting as close to as many of the huge crowd as he can. He is insisting on his human presence in this massive space, trying to obliterate the distances around him. As the crowd reach back out to him, it's a masterly, typically well-meant stadium entrance.

"I used to think this place was big," Grohl is soon considering, in the booming voice of a carnie huckster. "It's massive! I love it!" It makes me think for a moment, of course, of what it would have been like if Nirvana was playing this place, in this mood, 13 years on. There are allusions scattered through Foo Fighters' songs to the pain of that past, always tempered by positivity. "You just saved my life," as Grohl sings on "Best of You". The comparisons with his old band are in his favour in many ways. There is something redemptive and admirable in a man who went through such a grubby, globally picked-over trauma playing such relentlessly exuberant, indomitable music. It's preferable in spirit to Cobain's stomach-twisting, smack-flattened last days.

Exuberance, melody and galloping momentum are Foo Fighters' mode. Whatever the lyrical subtleties, the flat-out joyous emotion is permanently turned up to 11. There are few pauses for breath, or thought. If you're a fan dancing down the front, the constant pumping beat must be exhausting and ecstatic. But for me, the unvarying pace might as well be slow. When you stay at top speed, momentum goes nowhere.

"Long Road to Ruin" gives a clue to Foo Fighters' breakthrough to audiences that Nirvana never reached. It is one of several songs drawing on pumped-up, 1980s-style power ballads, part of the unhip US pop hinterland that Grohl, like Cobain, always loved. It's no surprise that he instructs any future rock stars in the stadium to watch a video of Queen playing Live Aid at this venue, to see "what to do".

"Stacked Actors", reputedly about Courtney Love ("I'm impressed, what a beautiful chest... you're just another ageing drag queen") starts a period of sustained, stimulating variety. Grohl's squealing guitar solo and Taylor Hawkins' extended drum solo suggests another model, Led Zeppelin. They lack the sonic invention, but gain in punk concision. Jessy Green's Eastern European fiddling on "Skin and Bone" and the Bruce Hornsby-like splash of Hammond organ on "My Hero" add to the late-blooming layers, as the sun sets and red light bathes the crowd.

But for all the head-banging effort, the unruly unpredictability of Foo Fighters' rock'n'roll heroes never arrives. I leave liking them, but feeling musically blank.