Having delayed their Glastonbury appearance by a year thanks to a back injury sustained by Bono – not, as some wag had it, by carrying the weight of the world on his frail shoulders – the sense of anticipation, for this writer at least, at the famed Pyramid stage soon dissipated into one of disappointment as U2’s set progressed through a rain-sodden Friday night. Glastonbury 2011 was a performance from a nervous band looking for all the world as if they were merely dipping their toes into the water of playing live rather than diving in to the spirited performance that they’d built so much of their reputation on. Perhaps it was the heralded protest that had been planned against their tax-efficient affairs, maybe it was the fact they were playing on someone else’s turf but, viewing their set from in front of the mixing desk, this didn’t feel like a band ready to take on all comers. This felt safe and measured and any notions of chances being taken were soon blown away with the rain the came down on Worthy Farm.

Tellingly, the opening five numbers delved deep into 1991’s Achtung Baby, an album that was to be re-issued later in the year with the full 20th anniversary fanfare. Adventurous on its release, this was a record that summed up the feel of the new eclecticism of the early 90s in the wake of rave’s first heady flush. With ecstasy culture going overground and being co-opted by the mainstream, Achtung Baby fused rock with loops, dance beats, drugs and industrial music. Moreover, the album hitched its wagon to the colossal social and political tectonic shifts that were shaking the world in the aftermath of the Thatcher-Reagan years. A period of seismic changes, the Iron Curtain fell as the Soviet Union collapsed, Eastern Bloc counties seized the chance for self-determination as the Balkans descended into war while in South Africa Nelson Mandela finally reached the end of his long walk to freedom and the first Gulf War unfolded on our TV screens. Elsewhere, the information superhighway was beginning to usher in the first flow of traffic that would alter the way that information was to be consumed. Musically, the two-pronged attack from Nirvana’s Nevermind and Primal Scream’s Screamadelica as well as REM’s storming of the international charts with Out Of Time ushered in a period that demanded you forgot everything you thought you knew.

Embarking on the Zoo TV tour in 1992, U2 changed the notion of what a stadium gig could be about. The packing of stadiums by rock bands, many of whom should have been put out to pasture, in the wake of Live Aid in the mid-80s, ensured that the medium became more about the event and simple entertainment rather than challenging the trappings of the outside world by transporting you to a universe at odds with perceived reality. Playing on a stage resembling some kind of cyber urban landscape, the production was characterised by TV screens, video walls, information overload, news bulletins and satire while the band themselves shook off the earnest rags that had clothed them in the previous decade to drape themselves in glamour, sleaze and irony. Though they may have stopped exposing their collective breast so their audience could feel the warmth of their sincerity, U2 nonetheless still had something to say even if the medium of their message had changed.

In the middle of this touring maelstrom, Zooropa dropped almost unexpectedly and with a fraction of the fanfare that had accompanied its predecessor. Recorded on the hoof during the odd day off during the Zoo TV tour and originally planned as an EP, Zooropa is the sound of U2 at their most audacious and daring. To these ears, this is their high water mark, an album that’s prepared to take chances and push the envelope, it builds on the foundations of its predecessor as the band challenges itself as much as its audience. They’ve never sounded as bold since and their wobble in confidence was evident in the aftermath of its follow-up, 1997’s Pop. By 2000, they were re-applying for the job of “The Biggest Band in the World” and, as evidenced by that lacklustre Glastonbury performance in 2011 and the albums released since the turn of the millennium, show no signs in wanting to rock the creative and cultural boat again. They’ve moved from rock aristocracy to rock royalty, and as long as they keep giving their audience what they think they need, the chances of them ever having such an impact beyond the box office remain slim.

It’s probably this kind of conservatism that has somehow led to Zooropa falling between the cultural cracks. Viewed from the vantage point of the 21st century, Zooropa feels like a prescient work that heralds a technological future where media overload and a lack of editing and processing skills have reduced the worth of information to so much white noise that’s culturally poor yet financially rewarding for those that control the flow. Indeed, to listen to the title track, now as then, is to view a world where the exchange of information becomes less about meaningful dialogue and the exchange of ideas to seek out a brave new world and more about the creation of demand for consumption. Stretched over two minutes, the opening of the title track feels more than a little voyeuristic as the sound of compressed and barely audible voices becomes apparent but less discernable. Are these soundwaves? A recorded conversation? Who’s saying what and to whom? The effect is not unlike the party lines from decades back that frequently plugged you into your neighbours’ conversations or, these days, like working for the NSA.

It’s been claimed elsewhere that Zooropa is a minor work by a major band and one viewed with ambivalence by its creators; that crucially, in terms of U2, it lacks a major statement. This is an argument that’s hard swallow, especially in light of opener ‘Zooropa’. Painting from a sonic palette that feels like an industrial take on Massive Attack’s timeless ‘Safe From Harm’, the song looks at a post-Cold War Europe straight in the eye and doesn’t like what it sees: “Zooropa – Vorsprung durch Technik/Zooropa – Be all that you can be/Be a winner/Eat to get slimmer”. Is this really what the Cold War was fought over? The right to be sold to and to consume? Wasn’t there supposed to be some kind of higher goal we were aspiring to? Is this all there is? This is as bold a statement as U2 have ever made but there’s also a knowing humour and lightness of touch that prevents it from sliding into pomposity.

This lightness of touch is also evident on the dance-inflected rhythms and pulses of ‘Lemon’. The standing joke at the time was that indie bands had always claimed there’d been a dance element to their music yet here was the biggest band in the world fully embracing the possibilities of operating way outside of their comfort zone and doing it convincingly. This wasn’t a case of say, The Soup Dragons, who remixed an entire album in one of the worst bandwagon jumping exercises of the era but a genuine attempt to move with the times and to alter the perception of both the band and its fans. Similarly, the industrial groove of ‘Daddy’s Going To Pay For Your Crashed Car’ – Larry Mullen Jr’s huge, processed drums and Adam Clayton’s filthy, grinding bass take centre stage here – sounds unlike anything that the band had produced before or since; within these grooves lie adventure and risk, a sonic exploration that deserves applause not only for its audacity but for its success.

There are, of course, nods to familiarity and so it is that ‘Stay (Far Away So Close!) and ‘The First Time’ are the ballads that sail closest to U2’s classic sound. But even here there’s room to scuff the songs around the edges, to make them aurally frayed and the effect is as compulsive as any of the songs on the album. Both songs are given a widescreen treatment not through bombast but by the application of ambient sounds that add an air of menace and uncertainty.

If any one theme comes to dominate Zooropa then it is that of uncertainty. The key lyric of the album, “uncertainty is a guiding light” on ‘Zooropa’ manifests itself throughout. The Edge’s deadpan and almost brainwashed vocal delivery on the electro-groove of ‘Numb’ brilliantly encapsulates the emptiness at the heart of consumer culture; that for all the participation in it, the rewards on offers are slender at best. Isn’t there something else? Shouldn’t there be something else? Zooropa doesn’t pretend to offer any answers but it does at least ask some very pertinent questions that, 25 years after being released, still resonate and are still waiting to be answered.

Mention must also be made of album’s closing number, ‘The Wanderer’. Featuring a guest appearance by Johnny Cash ahead of his career reviving series of American Recordings with uber-producer Rick Rubin, it jars against the rest of the album both lyrically and musically. Taken on its own terms, the song brilliantly and simultaneously embraces and subverts American vernacular and succeeds where ‘When Love Comes To Town’ fails but here we have a protagonist – a post-apocalyptic preacher - who, unlike the narrators of Zooropa’s other songs, has a clear sense of purpose and definition. The end result is a strange form of resolution that doesn’t sit entirely comfortably with what has preceded it.

With the benefit of 25 years’ hindsight, Zooropa can viewed as a transitional album of a 90s triptych that sits between Achtung Baby and Pop. While its predecessor ushered in a new era for U2 and its successor attempted to build on the technology and a desire to push the musical boundaries enforced around them, Zooropa remains the most fascinating listen of the three. Recorded under strenuous circumstances and against the clock, this is the closest U2 have got to anything resembling spontaneity. The mixed reception to Pop left the band battered and bruised and every album they’ve released since feels as if it’s playing to the gallery and seeking approval. They’re no longer shooting from the hip but simply trying to be hip and this corrosive attitude has led to music that lacks any real joy, risk or playfulness at its heart.

U2 are an easy band to smirk at thanks largely Bono’s extra-curricular activities but to listen to Zooropa is to appreciate a huge rock behemoth prepared to take a massive chance in an exercise that could well have blown up in their faces. When was the last time that happened? Too many focus groups and marketing teams erroneously treating their jobs like an exact science and too much money at stake has contrived to create an era of creative sterility among bands of a certain stature. Two and a half decades on and Zooropa remains not just their most intriguing listen but also their most fun. Heavy topics don’t have to be heavy-handed and it’s difficult not to pine for a band that plugged into culture on such a massive scale without wallowing in pomposity doing it. Four years down the line since the dreary and utterly forgettable No Line On The Horizon, the safe bet is that U2 will be meticulously planning their next move to the very last detail and the results will be every bit as tedious as that Glastonbury performance. No, for the opposite of all that gubbins, Zooropa is where it’s at. Remember them this way.