Ozzy Osbourne, Leas Cliff Hall, FolkestoneAl Green, The 02, London

Considering all he's been through, Osbourne makes a decent job of resurrecting the old hits

One unshakeable fact emerges as I revisit Ozzy Osbourne's back catalogue while the train rolls on towards Folkestone: I bloody love Black Sabbath.

It's all too easy to caricature Sabbath as pseudo-mystic dumbos, a Led Zeppelin for CSE kids, all upside-down crosses and Aleister Crowley, but find the footage of their early TV appearances and you'll see a straightahead, speed-freak, gonzo garage rock band, essentially a British Stooges, right down to their "motor city" origins.

When they came into their own, however, was when they killed the speed and locked into a sludgy, dinosaur-footed groove, like a diplo-docus wading to its slow death through the La Brea tar pits, as exemplified by "Sweet Leaf", sampled by the Beasties, Buttholes and countless others.

Sabbath exuded a specifically working-class strain of youthful nihilism, mistrustful of the treachery of the adult world, cynical about the employment conveyor belt, concerned only with making the rent, smoking weed and waiting for the apocalypse: "Hole in the sky, take me to heaven ..." And, in the forlorn, woe-is-me voice of Ozzy Osbourne, those sentiments had the perfect vehicle.

Taking the Ozzy Osbourne of 2010 seriously, however, is a challenge. It wasn't The Osbournes that blew Ozzy's gravitas: he'd already done that himself with his campy 1980s persona. But since that series, he's become a nationally treasured, substance-damaged jester, shouting "Sharooonnn!" in novelty greetings cards, rerecording "Changes" – Sabbath's suicidal end-of-relationship lament – as a soft-centred Father's Day gift, and appearing in the Beeb's appalling patriotic montage before England's World Cup humiliation.

He's got some ground to reclaim, and no mistake. And, to my mild surprise, the old man makes a decent fist of it. For starters, either I'm going blind, the make-up's thick, or the lighting's sympathetic ... or he really is looking relatively lean and healthy. Corpse-like pallor, black nail varnish, smudged eyeliner, maniacal grin: this is the Ozzy you want to see.

Admittedly, he does that doddery, confused walk familiar from his family's reality show. Admittedly, the guy sitting side-stage with the laptop, advancing the lyrics line by line for Ozzy's autocue, is a vital member of the crew. Admittedly, his slurring speech is difficult to decipher, besides a repeated "I can't hear you!" which, at his age, might be a genuine cri de coeur rather than showbiz banter. But his charisma is so strong it's ridiculous, and that voice is as magnificently mournful as ever.

Taking the stage in a diamanté-sleeved cape for "Bark at the Moon", he hurls bottles of mineral water into the crowd. Immediately, someone sprays the contents back at him, whereupon he roars "Let's 'ave a fuckin' war!", and retaliates with a whole bucketful, a stunt he repeats three times.

Solo hits such as "Shot in the Dark" and "Mama I'm Coming Home" are all very well, but I'm here for the Sab stuff, and tonight we get Beavis & Butt-Head favourite "Iron Man", "Fairies Wear Boots" (one of the brilliant Sabbath songtitles) and an encore of proto-punk anthem "Paranoid", whose opening line "Finished with my woman cos she couldn't help me with my mind" is a great blues lyric, never mind heavy metal.

It matters little that I'm not hearing it performed by original Sabbath personnel, nor even by long-time sidekick Zakk Wylde. Ozzy has easily as much right to these songs as Tony Iommi, who sullied the band's reputation in the 1980s by putting out "Sabbath" albums featuring just one original member: himself. These days, Oz is backed by three tattooed longhairs of above average competence, and a drummer whose riser, hilariously, is half the height of the room. And they're perfectly adequate. What's a guitarist anyway, except a hired hand?

He promises more songs if we "go wild", and I'd have sold my soul for "War Pigs" (if only to bellow along with legendary non-rhyme "Generals gather in their masses/Just like witches at black masses ..."), but the lights come up, so Folkestone must have failed to go wild enough for Ozzy's liking. Then again, maybe he just didn't hear us.

Of the great smooth soul lovermen, who have we got left? Marvin, Barry, Isaac, Teddy, all departed. Only two of the true giants are still standing: the divine Smokey Robinson, and the Reverend Al Green.

Nearly four decades after his commercial peak, the sharp-suited Rev, holding a rose in one hand and using the other to issue subtle fingerclick cues to his band, has apparently added telepathy to his talents. "I bet somebody here is wondering if the Reverend's still got it," he thinks aloud during "Let's Stay Together", and he's not wrong. To answer the hypothetical doubter, he effortlessly hits that "aaaaah!!!" top note, rips off his tux, tosses the rose aside and slays the place.

Religious conversion is often the result of trauma, and Green's own 1976 rebirth is said to have occurred after a girlfriend emptied a pan of hot grits over him in the bath, then shot herself in his bedroom. You know, therefore, that you're gonna get excerpts from the great God-bothering songbook ("Amazing Grace", "Nearer My God to Thee"), but nowadays Green wears his faith lightly, with humour even.

It's the immortal Willie Mitchell-produced classics such as "Tired of Being Alone" that we godless Brits long to hear, however, and Al obliges, inadvertently providing the answer to his rhetorical "How Can You Mend a Broken Heart?" Listening to Al Green ain't a bad place to start.

Next Week:

Simon Price watches Arcade Fire launch their third album The Suburbs in inner-city Hackney