It's the injustice that grates the most, really. Eighteen months ago, on this very stage, a much-touted rapper by the name of Mathers turned in a dull, uninspired six song set that reflected poorly on his recorded output and left most in the audience wondering how he'd ever earned a fearsome reputation for freestyle rap mastery.
Tonight, a rapper every inch the equal - if not the better - of Slim Shady delivers line after line of battle-hardened, cynic-defying, sometimes even jaw-dropping lyrical invention, confirming that the hype and hullabaloo that accompanied his emergence in 1997 was justified. Yet Eminem will spend Christmas at the top of the charts, while Canibus tours some of Europe's more intimate venues, as yet unable to turn underground adulation into mainstream success.
It's desperately unfair, and the comparison - though Canibus speaks very highly of his former battle and mixtape cohort - is unavoidable. Both Em and Bus came up through the ranks of rap's unforgiving live environment, getting up on stage and outwitting competitors with quickfire rhymes and improvised lyrical bodyblows.
Yet while Mathers hitched his talents to Dr Dre, and some of the most pop-friendly hardcore hip hop beats of the '90s, Canibus made a debut album that, despite selling half a million copies, he's now so unhappy with he refuses to acknowledge it as part of his discography. So for tonight's show - somewhat astonishingly Canibus' first bona fide UK live appearance, other than a brief cameo during a 1998 Wyclef Jean gig - draws almost exclusively on his second LP, '2000 BC'.
What strikes you most forcibly about Canibus live is how clear and strong that razor-sharp voice of his is. Where most live rap falls down as emcees mumble into their chests and sound engineers wrestle gamely with feedback levels, it's clear the chap his mum calls Germaine Williams has arrived at his vocal style because he's found that it works well live. Even so, when he has new material to deliver, he does it a capella, turning the event into something akin to a boisterous trade union meeting as he carefully enunciates his long-awaited riposte to this summer's escalation of his celebrated war of words with LL Cool J.
Maybe Canibus is too clever for his own good. Maybe he's even too good for his own good. Eminem has succeeded by feeding the public a lowest common denominator diet of sex and violence, which has become as identifiably a part of his recording personality as his blonde hair or nasal voice. Canibus' raps are for the devotees, for people who like to pick apart every line to find Shakespearean levels of hidden meaning, and taking cheap shots - even when belittling LL - is never an option.
You've got to hope that a place can be found at pop's high table for a performer as skilled and as fiercely intelligent as Canibus. Time is on his side, and he's really only one lucky break - a catchy tune? A track with a singalong chorus? - away from smashing things wide open. But for the time being he remains a frustratingly small distance away from the prize he so richly deserves. Sometimes the music business, just like life, really isn't fair.
