The Stone Roses, Heaton Park, Manchester Nicki Minaj, Hammersmith Apollo, London

Despite the latter-day sainthood heaped upon them, the C-word still applies – conservative

'We've still got it,' declares Ian Brown last night in Manchester (Rex Features)

I was there, and as long as I live, they can't take that away from me. Oh, I'm not talking about the Heaton Park reunion of 2012, the memory of which will soon fade like a yellowing music paper. Nor even Spike Island in 1990, their first tribal gathering, in the shadow of Widnes's chemical chimneys.

No, I was there the last time The Stone Roses, by then reduced to frontman Ian Brown, bassist Mani and a motley rag-bag of ringers and Simply Red session men, played to an English field. Their final UK performance before splitting, at the Reading Festival in 1996, was so infamously atrocious that statues covered their ears.

In the intervening years, a weird kind of sainthood has descended on the Roses, their myth somehow undamaged by the dull solo careers of both Brown and guitarist John Squire. So, let's get this right: The Stone Roses were a comfort blanket to a drug-damaged generation that woke up one acid-ravaged Eighties morning sobbing for the familiarity of a bog-standard guitar quartet. For a band whose main innovation was wearing white instead of regulation alt-rock black, they did a fine job of building a mystique, assisted by a guitarist who dabbled in action painting. But never mind the Pollocks: their sound, at best, recalled The Hollies and, but more usually, Herman's Hermits. The Stone Roses were as conservative as they come.

Nevertheless, this year's three reunion shows sold out in record time, although their comeback has not proceeded without rancour, inside and out. Brown used the C-word about Reni onstage in Amsterdam after he failed to show up for the encores. Meanwhile, the NUJ has backed a photographers' boycott of Heaton Park after snappers were initially presented with a contract under which the Roses would have exclusive rights to all pictures in perpetuity for the nominal purchase fee of £1. This from the band who famously fought a legal case against Silvertone for ownership of their own work.

By 9pm Heaton Park is awash with beanie hats and lager, looking like some apocalyptic wicket-keeper's convention. But as The Stone Roses open with "I Wanna Be Adored", there's something undeniably affecting about 72,000 people chanting along, something poignant about the impossibility of that desire. Not everyone can be adored.

After weakling early single "Sally Cinnamon", Brown, pacing the stage in a leather jacket and low-slung denim like he's looking for a fight, brags: "As you can see, we've still got it." If he means they're unchanged, he's right. Brown, specifically, is the foghorn he always was. It's not just that Ian Brown is a bad singer. There are good-bad singers (a category into which many of my all-time favourite vocalists fall), and there are bad-bad singers. Ian Brown is an awful-bad singer, owner of a characterless, can't-be-bothered, tone-deaf drone. For the first few songs he holds the tune, drowned out in any case by the throng, but by the end he's way off-key.

Lyrically, too, their works are as laughable as ever. "Elizabeth My Dear" is dedicated to "the dirty parasites 200 miles down the road, celebrating 60 years of tyranny", but the lyric – "Tear me apart and boil my bones/I'll not rest till she's lost her throne/My aim is true, my message is clear/It's curtains for you, Elizabeth my dear" – makes E J Thribb look like William Blake. Brown's rapping on "Love Spreads", stealing a verse from Eric B & Rakim's "Paid in Full" then adding "Stone Roses, all the rage/Stone Roses, on the stage" is even more laughable.

Once or twice, though, the Roses transcend their limitations. "She Bangs the Drums" is an undeniably brilliant pop song. And it would take a joyless man not to groove to "Fool's Gold", used tonight as a showpiece for John Squire to show off his muso chops, as is the finale of "I Am the Resurrection". As that song ends, Brown brags again. "Not bad, for a bunch of old ...." I'd go along with that, but no further.

After an enjoyably preposterous entrance dressed as a sorceress in a temple of fake fire, Nicki Minaj whips off her cloak to reveal a day-glo green top and pink hot pants.

A million words have been written about the Minaj behind. Her prominent posterior is, she insists, Mother Nature's work alone, not surgically enhanced. In many ways, Nicki's backside is the Minaj phenomenon writ small – or large – her success being a mistressclass in working what you've got. The Trinidadian 29-year-old, discovered via MySpace, was signed up to Lil Wayne's Young Money stable alongside Drake, and now threatens to eclipse both male rappers.

It's difficult not to be swept up by the hysteria of a young crowd in the presence of someone whose moment is clearly now, not in some dead, draughty arena next year.

Minaj is, if nothing else, a pocket dynamo onstage. Then again, it's easy to be energetic when you aren't actually singing. Rumours of Minaj's miming are at first hard to verify, but before long, she removes all doubt by talking over her own "vocal". She's so unconcerned about even pretending to hold the microphone near her mouth that it borders on subversive.

But this is as much a costume drama as a pop concert. Midway through the second song, a wardrobe assistant visibly wheels a groaning clothes rail into the wings. If it's gonna be a long night for all of us, it'll be even longer for him. ("It's the third interlude? Must be time for the Monroe ….")

Minaj's multiple personalities, à la Beyoncé's Sasha Fierce, are well documented, but that doesn't make them less baffling. "Are you wondering why I'm doing this weird Marilyn Monroe voice?" she asks, in a weird Mary Poppins meets Patsy Ab Fab voice. Ronni Ancona won't be losing any sleep. Her other selling point is rudeness. A typically charming Minaj verse runs "Man, I just shitted on 'em/Shitted on 'em/Put your number twos in the air/If you did it on 'em".

That aside, what has she got? A couple of dozen perfectly decent R&B jams, and the odd blast of Katy Perry Euro-pop delivered with boundless bounce. "If you're happy to be alive," she urges, "scream!" Is it bad that I hesitate?

Critic's Choice

Scottish megafest T In the Park features Snow Patrol, the Stone Roses, Kasabian, New Order, Noel Gallagher, Nicki Minaj, Skrillex and the Horrors, at Balado, Kinross-shire (Fri, Sat, Sun). On the same dates, boutique festival Lounge on the Farm has a line-up including Dexys, Chic, Emeli Sande and Niki & The Dove to Merton Farm.