It's a hugely anticipated show. Jane's Addiction have only played two shows outside of the US in 11 years. The touts' starting price is only £100. Things get even more absurd when I wander in the toilet to find an attendant trying to powder me and douse me in cheap perfume for loose change, as if the grotty Forum were some high-class hotel in elite inner city London.

But what about the band? When they formed in 1986, their contemporaries wore spandex, played formulaic, pedestrian metal, and sang about girls girls girls. In the meantime, Jane's did metal - but played it like jazz. Freeform, improvisatory, shifting tempos and styles from minute to minute, extolling the virtues of mind-altering substances and deriding the hypocrisy and wreckage of capitalism with an authenticity that could only come from experience. "Everyone's the same when you're a whore".

In the past fifteen years they've written one new song that I've heard. And this brings us back to the beginning. An impromptu encore sees them unleash "Hypersonic" - a veritable tornado of sound that resembles an amphetamine-crazed version of "Stop!". The band whirl around the stage like hyperactive teenagers and Perry Farrell yells out the words as if his very life depends upon it, kicking over near enough anything he find out of the way - drumkits, mikestands, amps - in the process.

The rest of the set sees them hailed as returning heroes, even though this isn't really Jane's Addiction anymore. Chris Channey, ex of Rob Zombie and Alanis Morissette duties, is a plodding anonymous session bloke on bass, and an equally characterless "John Doe" - behind a superfluous keyboard set - seems to be slowly turning Jane's into a huge Pink Floyd style ensemble. They even cover a Floyd number in the middle of the set.

And there's stadium rock pantomime. Perry wanders on stage looking like an angel, decked out in white faux-fur and a hat worthy of the front page of an overpriced fashion magazine. For the encore he's done a costume change in so much as he looks like an enormous walking flower. It's not rock n roll - it's theatre. And his stage raps - all about "youth on the move" and Aphex Twin are precariously old-fashioned but oddly charming. At one point he even comes forward and asks if the band are projecting correctly.

But if you close your eyes this sounds like the best band in the world. Even if they are plagued with technical problems that often render the vocals and guitar inaudible, there’s nothing like hearing 2,000 people chant “all of us with wings!” with semi-religious fervour during the ninth minute of the taut, ambient-prog-rock-drum-solo-thrash-metal epic that is “Three Days”.

But with only one new song to show for the past 15 years, you can't help but wonder, despite their obvious greatness, if they've still got the essential spark of genius they once possessed so briefly.

Do yourself a favour. Buy the albums. You'll thank me later. I promise.