Mos Def, The Forum, London

Hip-hop has evolved so much in the past decade that it's hard to tell what makes the definitive rap fan. At one end of the spectrum, you have the rowdy types, who'll happily chew off their legs for the opportunity to pump their fists to the euphoric triumph of MOP's "Ante Up". Then there's the new rap intelligentsia, motivated to wax lyrical about social injustice and the politics of love then reel off their various sexual exploits as if they've been knocking back jars of Viagra. At one point, Mos Def pleased both varieties, offering his weighty rap roots and enlightened persona which validated him as one of the performers who could sing or do anything he pleased. Major label defiance? His rock project The Jack Johnson band. Alternative income stream? The Hitchhikers Guide to the Galaxy. Moral relapse? "Drunk and Hot Girls" with Kanye West.

Yet despite his reputation for endearing eclecticism, Def's first London show since 2007 is still confusing. The pitch is neither too ambitious nor lazy, and his opener, "Supermagic", could have summoned roars by virtue of its rebellious intro. The rapper mysteriously appears behind his drum kit, beating away without a care in the world, but for all its boisterous intentions, it's pretty anticlimatic. The bass-heavy "Twilight Speedball" follows as he casually strides into full view, but by the fourth song, "Auditorium", the crowd's unease hasn't quite lifted (no thanks to the shambolic sound and the accompaniment of two DJs, when really a band should have been recruited) and you wonder if for all his smiling and skilful dancing, he's clocked the number of blank faces merely staring back at him from the audience. "Y'all are so polite," he concedes, then returns to enjoying himself as he reels off songs from his latest album The Ecstatic, which the bulk of this crowd hardly know.

To be fair, the rapper/actor almost has it all – humorous charm, his unique enthusiasm, politeness, a smidgen of creativity – although switching between drums and dancing centre stage while gripping an old school microphone borders on contrived theatrics – and he's even got Amy Winehouse, Mr Hudson, Master Shortie and Shingai Shoniwa of The Noisettes in the house to cheer him on. But the few fans in the front row who must have had him convinced everything was going well should have urged him to turn up the energy level a notch and choose some of his most notable songs from his debut Black on Both Sides and his noteworthy cameos with modern soul survivors like Jill Scott and Bilal. He eventually saves himself from totally flat-lining with a quality tribute to Michael Jackson (with moonwalk to boot), and vigorous performances of "U R The One", "Definition" and finally "Umi Says". There's even a hilarious nod to Eddie Murphy's Coming to America, with his rendition of "The Greatest Love of All". But if Mos Def is looking to lead hip-hop into a realm of conceptual art where he plays by his own rules to the detriment of his loyal fans, plenty of these folks would have appreciated being warned first.