Spice Girls, The O2, London

What they really, really want is grown-up fans

The woman next to me is 20. She is wearing a spectacular outfit finished by purple glitter boots with seven-inch platform soles. She describes herself, with knowing humour, as an "aspiring Ginger Spice wannabe". She has been waiting for this moment for half her life.

Growing up in a working-class community in the North-east, she and her friends would perform Spice Girls routines in the street. "Any child at that time could relate to at least one member," she tells me. "They were like superheroes, but at the same time they were real life, not fairy tale."

Girl Power rhetoric, she believes, had a lasting effect on her generation. "They got me thinking 'I don't need a boy', yeah. They're probably responsible for me not being a teenage mum."

This is why I do not sneer at the Spice Girls. Manufactured and marketing-driven they may have been, but Spice Girls nevertheless took a broad-brushstroke, capital-letters version of feminism to a demographic which, for reasons of age, location, class or taste, was never going to engage with campus-based scenes built around scratchy indie singles.

It's also why I can't entirely begrudge their launching this reunion tour before Posh looks too much like a melting waxwork. Spice Girls were a great pop thing.

Rising up on individual plinths, kitted out in beige and gold (Scary in giraffe print, Posh in spray-on PVC), they instantly remind you of their weaknesses. "Spice Up Your Life", a song that tops and tails the show, still baffles with that racially questionable lyric about a "yellow man in Timbuktu". The needy "Say You'll Be There", the kickass martial arts moves in the vid notwithstanding, shows their autonomy had limits.

The burlesque jazz choreography for "Lady Is a Vamp" works well, but the show slumps in places, for example "Headlines", the turkey of a comeback, and a time-wasting disco medley. And those ill-chosen solo spots: Beckham with a catwalk/paparazzi skit (should have been "Out Of Your Mind"), Halliwell with "It's Raining Men" (not "Look at Me"), Mel B with Kravitz's "Are You Gonna Go My Way?" (not the Missy duet "I Want You Back"), Mel C with "I Turn to You" (not her Pistols cover). Only Bunton nails it with her Sixties routine for "Maybe".

The post-Geri material merely proves that her departure was the downfall of both parties. She shrivelled from curvaceous goddess into hard-bodied yoga monster; they limped on for one forgotten album before splitting unmourned. And tension remains: "You even made Victoria Beckham smile," Ginger jokes at the end, with just a hint of bitterness.

The low point comes during "Mama", when the five are joined first by an enormous children's choir, then by their actual kids. Sick bucket, please.

That said, "2 Become 1" still sparkles and "Who Do You Think You Are", accompanied by costumes from their pomp phase (minus the Buffalos), is vibrant. I ask the woman next to me what she made of the show. "It exceeded all my expectations, considering how long it's been. Shame about the lack of platform boots."