Massive Attack, Brixton Academy, London

Massive Attack have been shaken almost to pieces in recent times. First, one of their central trio - Andrew "Mushroom" Vowles - left for good, then Grant "Daddy G" Marshall absented himself from the studio, leaving Robert "3D" Del Naja to assemble the first average Massive album, last year's 100th Window.

The disgraceful slurring of Del Naja with unfounded allegations of accessing child porn, just as 100th Window was released - and, some noted, as he made himself a vocal opponent of the Iraq war - only added to the band's embattled status. If, as Del Naja often states, Massive Attack is a brand, the name for a largely unrecognised collective of shifting personnel and musical styles, then that brand is weaker than ever before.

Once untouchable masters of a claustrophobically beautiful musical kingdom all their own, ever since their deified debut Blue Lines (1991), 2004 finds Massive Attack very much earth-bound, with a reputation to reclaim. At least they have safety in numbers again, as the tall, rangy G takes to the stage with the slight 3D and Horace Andy, the light-voiced singer who connects them most closely to the Bristol reggae blues nights of the Eighties where the band first came together.

They are greeted with a friendly cheer, not the roar reserved for conquering heroes, and the subsequent applause rises with the age of the songs, in a set that, wisely, draws heavily on 100th Window's great predecessor, Mezzanine (1998). The backdrop is minimal but effective - glowing bars of light which turn into subliminal neon messages. But mostly the stage stays in shadow, suiting the understated, crepuscular sounds that Massive Attack conjure tonight.

Andy takes centre-stage for "Angel", followed by a heavy dub excursion that ends in a shriek. 3D meanwhile murmurs raps and adds harshly scraped guitars and snapping wood-block beats, the jagged irritants which stop Massive Attack sinking into trippy inertia. There are acoustic folk elements too, mostly added by guest vocalist Dot Allison, standing in for Liz Fraser on the Cocteau Twin-like "Teardrop". It's still an accumulation of sounds like no one else's, thick and heavy but with leavening flashes which stop it ever being oppressive. It's music which makes few melodramatic gestures, instead dragging you in almost subliminally, till the beats are thundering in your brain.

No one dances to this so-called dance music, instead bending their heads to its weight. It's also music which is undoubtedly designed to be chemically enhanced, and the parade of thirtysomething drug casualties, as well as the blatant E dealers creeping through the crowd, show the generation Massive Attack still speak to.

Accordingly, Blue Lines' "Hymn to the Big Wheel", with its sunrise sense of coming up on Ecstasy, gets the biggest cheer, at least until the inevitable encore of "Unfinished Sympathy". With its acid house keyboards and soulful vocals, it's a reminder of days when Massive Attack seemed untouchable. Those days are gone, but they are still something special.