So you finally meet The Great and Powerful Oz. And it turns out he's just a little jizzim with a God complex, like Jeremy Clarkson's mini-me, or Richard Hammond, as he's known. Well, seeing Death Grips live for first time, that's my Oz moment. MC Ride... the beast I worshipped.... turns out he's just a man. And it's disenchanting. It's the first time you watch The Phantom Menace, or catch your Dad stealing biscuits from the forbidden stash, or walk in on your brother shaving his legs 'cause he wanted to see what it felt like to be a woman, just for a day. Disappointment is a cruel mistress, like your brother dressed as a stern Weimar-ian hostess when all you wanted to do was play football in the garden.

For me, The Wizard Of Oz has always been a tad anti-climactic. I've always been more of a Return To Oz type person. In Walter Murch's disastrously misjudged 'children's film', the 'Nome King' has reduced The Emerald City to a Hiroshima-like aftermath zone (complete with fossilized victims), now ruled by Mombi, a head-exchanging witch and the most inappropriate creation to ever grace a PG. Hoodwinked by the Disney banner and glad to be reliving fond childhood memories, in good faith it was my mum who brought me to the matinee. Ten minutes in and Dorothy is institutionalised and scheduled for immediate electro-shock treatment. By teatime the saintly Veronica Calvert was a jaded shut-in with an irrational hatred for Paul Daniels.

Naturally, as a six year old this particular cinema experience was bewildering. Years later, though, the film fascinates me, with its themes of childhood's end and the parallels it drew with Reagan's 80s and the destruction of American ideals. The character of Tik Tok, the windup automaton always at risk of running down, seems now a poignant metaphor for man's powerlessness against the march of time. Something like that, anyway. What I'm saying is, Return To Oz was the adult truth to a technicolor fantasy, just as on a long enough timeline every chirpy indie band you once liked becomes a trivial, placating and utterly dishonest solution to the problem of living. You'll gravitate towards artists who embody that Jung quote I once read. On Brainy Quotes.com. "He who has not passed through the inferno of his passions has never overcome them."

Up until tonight, Death Grips were my Return to Oz band. They made amends for all those insufficiently nasty punk bands who never quite got to the cold heart of the truth. Or at least one possible truth, but one which music largely avoids. This being the truth of hatred, obsession, self-destruction and, above all else, what for the majority of human life is the hellish reality of living - in Death Grips' case a lifetime in Sacramento's crushing projects. In turn, it is the truth of my shameful pleasure in that suffering, as a voyeur. Death Grips are anti-pleasure, and if the 70s had The Pistols then DG summon new monsters, worthy of more terrible times.

So understand that, for me, Death Grips were it. They were playing my song. Swans + Public Enemy + horror rap x the FUTURE of punk. Since the brilliant 'Guillotine' I've written thousands of words about them, in countless articles, and each time I've stumbled on a new way to understand them. And rest assured I'll continue to write about their future records with fascination. But, while it's possible my expectations were too high and my preconceptions of how the show was supposed to be, too rigid - for me Death Grips live is a massive disappointment. Cue the nitpicking.

Cosmetically speaking, the show is perfect. When they begin, my head is touching the ceiling of the hall. I'm stood on seats in the annexed upstairs gallery, a glorified scaffold which shares its ceiling with the cavernous main hall. So, leaning towards the hall, through the windowless frames, the effect is vertiginous. I feel like Roddy McDowell in the Poseidon's upturned dining room, only less helpful. If I were a film director I'd place the camera right here. Because from here I get a great view of the churning mass of skulls as they go from black to red, as the stage turns to blood. The sense of occasion is insane. The scenery is minimalist, consisting of Zach Hill's drum kit and a black-clothed table, on which sit two computer monitors - side-decked like a couple of 2001's monoliths. Somehow the association makes sense, aesthetically speaking, what with the music's thematic tension between devolution and a kind of digital biomorphism.

Without ceremony, and with his locks shorn to near baldness, Zach Hill takes to his kit and plunges into one of his Slayer-on-Sunny Murray drum solos, which is only fractionally as thrilling as when Stefan 'Ride' enters left of stage. His face a lightless void in the backlighting, his punished physicality cut into impossible angles, he is a senseless malignancy forged from hillbilly slurs, from the fear of the other, from urban spook stories, from the ashes of the crucified. Maybe that's stretching it a bit, but fuck does he cut a singular figure in hip-hop, the closest thing music has to a real-live boogie man; the living embodiment of William Gibson's 'semiotic ghosts'. For a long time he just stands, as if suspended by an invisible noose, as if drawing energy from the pulverising drums and the machine gun strobe lights, and the general pandemonium out front. And hark, God did raise the man from the dead, freeing him from the agony of death, because it was impossible for death to keep its hold on him. I nearly did a jobbie in my replica Calvins.

Then the music starts. And it's No Love Deep Web opener 'Come Up And Get Me'. Soon after come the problems.

At first I think it's a volume thing, seeing that I'm right at the back. And I'm half right – even when I make it to the front rows 'Come Up And Get Me''s normally quaking bass seems puny. Before long, though, it's clear that the problems lies with 'loudness' of their art. The effect is strangely muted. There ought to be monsters.

I have my theories. A major factor is the absence of tech-man Andy Morin, tonight replaced by a backing track. It's possible they lacked the funds to bring Morin touring. But right off the bat, without the option to change gear, roll over, strike, creep, push and pull... to manipulate, they've lost the element of surprise. Which is more or less fatal. Because what we're really talking about here is the absence of chance, and so chaos. And when it comes to music, when we say chaos we actually mean anarchy. Which, decades on from the Pistols remains the true currency of cultural destruction. But everything here is so wrong. The creation of new myths has nothing to do with this degree of routine; a karaoke routine. The potency of a sharp but unfathomable version of psychedelia - the first time those people saw the Pistols; that was the expectation. I came here to see a concept in motion, not the act. I'm talking about the confusion of chance - that first disorientation that becomes a spiralling beyond reason, and which when it stops moving then hardens - and finally you're changed.

Death Grips fail to create an environment, a 'situation', because they're in 2D and meeting you narrowly. Put simply, there is a mundane symmetry to their live sound. Hill's interplay with the backing track, all counter-rhythms and triple-time rolls, creates the illusion of expressive freedom. In reality it's superfluous embellishment over a square re-enactment of the album. The sound remains inelastic. It just doesn’t breathe.

Countering the predetermined feel, Hill strings the individual tracks together imaginatively, the continuous flow producing a sustained tension and setting a relentless pace; punk pace. But there's pace and then there's penetration. Working off a stripped-down kit, the drummer delivers the album's kick hits with gratifying force. But the rest of his playing is focussed on the top shelf, nimble in a bad way, and conducted on aridly-pitched snares that sound almost like bongos, lending a reedy weakness to proceedings. And, while nobody wants a Bonham-esque rockist in the room, where the shit are the crash cymbals? No Love Deep Web's monumental 'Lock Your Doors' seems slight, while 'No Love', the album's other leviathan, seems somehow muffled. It's painfully unsatisfying. I'm so antsy. I'm pining for a wound. Give me timpani orchestras, power tools, the black box recordings from a thousand mid-air collisions. Anything. Because the only cure for fear is more fear.

The reason I know the problem lies with Death Grips, rather than the system or the venue, is because I have a yardstick in The Bug who, with a deadly understanding of space and combustion had, 30 minutes prior, shown the Ballroom the true meaning of power. I also can't help but compare it to the experience of seeing Swans, who do for mid-capacity venues what Carrie did for gym halls. Only because, listening to their albums, I assumed DG would be operating at this level. Alas, no. Without this ecstasy of body trauma I can only thrill to the groove. It's no coincidence that the dance tracks like 'I've Seen Footage' are the biggest hits with the audience. It should have been rage that 'liberated' the crowd. Instead we boogie unchallenged, in mindless accedence.

Then there's the Ride problem. He may look like a Gordon Willis-lit golem but his vocals are less compelling. Live rap shows are often hobbled by, well, the rapping. Without retakes, vocal processing (an untreated mic is surely hip-hop's greatest foe) and in general the controlled environment of the studio, coupled with the often flawed mix-balance between rapper and live production, frequently the double exertion of mellifluous cadence and tongue-twisting speed translates as indecipherable breathiness. Essentially, live rapping is a drably organic, imperfect and luddite defect in the presentation of an otherwise futurist genre. The thing is, on wax Ride's robotic style is more penetrating for its stabbing nature, and more manageable for a live rapper by virtue of its shouted flatness. So I assumed it would transcend the usual pitfalls; a post-human solution to the problem of human frailty.

Not so. Turns out, he's just a man. Pow wow dancing and buckling in funky waves, all the while he's missing words and losing voice projection, and his foothold in the mix is slipping… So he's ranting about the broken angels on his fingers or, like, the best way to execute a dog, but what we hear is “Paroop oop, brah, [breathing] ooh ooh [breathing] ughhhh [inaudible] KILLA!" It’s always pissed me off that Burnett's style is labelled artless or blank or un-narrational, by virtue of its mechanical nature, when actually it's overflowing with nuance and accent and emotive expression, making it a frighteningly effective vehicle for communicating wrath. I'm always reminded of Chuck D, who frightened the white establishment as much for his seething drawl as his rhetoric. But with the vocals tonight compromised, so too is the primary source of their sound's malevolence - it's ability to offend, and therefore its ability to move you.

Burnett's turn tonight follows in the tradition of performance-as-trance - and how often do you encounter that these days, in hip-hop or otherwise? - while I never lose sight of the utter strangeness of this music, in the greater hip-hop context. When we now have a rapper whose idea of a 'hater dis' is threatening to 'take his face off', can we not assume that even just a tiny component of hip-hop has altered irreversibly. I think so. I also think that if Death Grips are in fact the neo-punk second coming, then like The Pistols or Public Enemy, their battle will first be won on the ground.

A Note From The Quietus: During Death Grips' set The Bug vocalist Miss Red made an impromptu appearance on stage, and proceeded to dance behind the band to the left of the stage. After several minutes, with considerable force Burnett pushed Miss Red towards the back stage area, in the process knocking the 19-year-old off her feet. The day after the show we contacted The Bug (Kevin Martin) to get his views on the incident. Kevin replied saying there was "absolutely NO excuse for physically shoving a young girl." He also reported that Burnett had apologised profusely, immediately after coming off stage, and that Miss Red had accepted his apology. Kevin also told The Quietus that, shortly after the incident, Miss Red has assured Martin she was "totally cool about it" and attributed the incident to Burnett being, in her words,"in his zone".