Jay-Z, International Arena, Cardiff<br/>Wu-Tang Clan, Shepherds Bush Empire, London

Live performance was never the rapper's strong point, but he has confounded his critics by reinventing himself as a class act

How much significance can you read into a pair of glasses? A couple of weeks ago, Jay-Z turned up on the Jonathan Ross show studiously bespectacled, with the dress sense and demeanour of an amiable college-boy slacker rather than Roc-A-Fella CEO, rap megastar and bling-bling billionaire.

It was also one hell of a turnaround: the king of shopping- mall rap who has done more than anyone this side of P Diddy to cement the public view of hip-hop as a world of rapacious capitalism suddenly presenting himself as a cuddly intellectual, one of us.

He carried it off, just as – by common consent – he carried off his Glastonbury headlining set, which had the likes of Noel Gallagher in such an apoplectic tizzy beforehand.

The Jay-Z who shows up in Cardiff sure looks like the familiar bling-merchant: the hinges on his ever-present shades have more carats than Bugs Bunny, and the chain around his neck is more than merely goldie-lookin'.

Tellingly, Jay-Z had admitted to Ross that many rap acts make their initial breakthrough with one studio-forged track and, unlike rock bands, have no schooling in the art of the live show.

Indeed, last time I saw Jay-Z himself, he filled Wembley Arena with deadening thuds and bovine bellows. Not any more. He's learned a few lessons in the intervening years, and he's ready to deliver something that's only just short of a masterclass.

You have no idea how much it hurts me to say this. After all, I came to bury Jay-Z, not to praise him. This is a man whose main contribution to 21st-century culture has been to pop up on singles by Rihanna or Beyoncé, mumble lazily for 30 seconds or so and take a million-dollar cheque. (We get abridged bursts of "Umbrella" and "Crazy in Love" tonight.)

His excellent ensemble slide seamlessly between Latin hustle and funk-rock, incorporating teasing snatches of Amy's "Rehab", The Prodigy's "Smack My Bitch Up", Tribe Called Quest's "Bonita Applebum" and AC/DC's "Back in Black".

The high-speed interplay between the main man and his sidekick Memphis Bleek is often dazzling and, in the flesh, a track like "99 Problems" just cannot be argued with.

Just when you're wondering what the point of showing Damien Hirst's diamond-encrusted skull – one piece of bling the Jigga doesn't own – on the big screen might be, and cursing his audacity for name-dropping Public Enemy's Nation of Millions, he ties them both together in a passage about Hurricane Katrina.

A montage of American presidents freezes on the image of GW Bush, and Jay solicits boos, before rapping unaccompanied: "You're up on the roof/A helicopter swooped down with a telescopic lens/Just to get a scoop/But they didn't scoop you..." This time, the screen freezes on Barack Obama, and Jay-Z whips up the cheers.

From the high street to the hardcore. When the Wu-Tang Clan invite Londoners to throw their piece/peace in the air, it comes as a relief in the current climate that fingers and phones are all that are thrown.

But the mood inside Shepherds Bush Empire is pure joy, and not without reason. Assembling the main players of the Wu-Tang Clan in a studio – as Rza did for this year's first-class 8 Diagrams – is one thing, but getting them to put aside their differences and share a stage is quite another.

Cowled, scowling and overstaffed, the Staten Island collective looked a motley bunch when they dropped their astonishing debut Enter the Wu-Tang (36 Chambers) in 1993, but 15 years later, each of these men is emperor of his own domain.

Cappadonna is absent tonight as, for obvious reasons, is ODB, but the original Wu are otherwise present and correct, if slightly chubbier (Raekwon) and balder (U-God).

If one Wu warrior carries this reunion, though, it's Method Man. From the moment he rips off his hood like a heavyweight boxer, Meth oozes pure charisma and keeps up a level of energy (eyeballing the front row and embarking on his famous crowd-walk) that shames his more lethargic colleagues into raising their game.

Outside the Empire, bow-tied Nation of Islam emissaries make token attempts to hawk the Final Call newspaper, resigned to the fact that – for all Rza's dire warnings about dealing with white "devils" on his new Bobby Digital album – the Wu have gone the way of all "heritage" hip-hop acts: their audience is now predominantly old, sensible and, well, Caucasian.

What's gone on inside is far more startling: 11 legends beating indolence and indifference – their own, as much as anyone's – to prove their mettle. Consider da m-f ruckus well and truly brought, once again.