Touring in support of its first two albums in the new millennium, the unadventurous U2-by-the-numbers “All That You Can’t Leave Behind” (2000) and “How to Dismantle an Atomic Bomb” (2004), Bono and the boys were in danger of becoming their generation’s Rolling Stones—a rote if occasionally rousing arena act more devoted to selling tickets than to breaking new musical ground.

Released last February, “No Line on the Horizon,” the Dublin band’s 12th studio album, came as a welcome surprise: Though they didn’t always succeed, the musicians at least took chances again, veering from that familiar U2 bombast to deliver their most creative disc since “Achtung Baby” (1991). Unfortunately, the new album also has been the slowest selling of their career, with U.S. sales yet to reach platinum status of a million sold—a fact that can be attributed to no one buying CDs anymore, or to fans being turned off by the group’s experimentation.

Eighteen years ago, “Achtung Baby” inspired the Zoo TV Tour, a multi-media sensory assault that stands as the most inventive arena jaunt I’ve witnessed. The question looming over Soldier Field Saturday night as U2 launched the North American leg of its 360° Tour at the first of two concerts in Chicago was whether the band would uphold the creative spirit of the new album, matching or topping Zoo TV, or play it safe in an attempt to reconnect with conservative fans and please its new partner, giant national concert promoter Live Nation.

The answer, as is often the case with this band, was that it tried to do it all and please everyone. Though it avoided the most ambient and atmospheric of the new tracks crafted with Brian Eno and Daniel Lanois, the group did play a hefty chunk of “No Line on the Horizon,” including the strong show opener “Breathe,” the hypnotizing “Unknown Caller” and the soaring “Magnificent,” which really was.

But in place of the disorienting buzz of Zoo TV, U2 gave us the empty spectacle of the multi-million-dollar stage fans have come to call “the Claw,” a ludicrous, fog-belching, crab-like mega-structure that primarily succeeds in dwarfing the musicians onstage, recalling David Bowie’s equally silly Glass Spider Tour and making recent Stones stages seem modest in comparison. (U2 really ought to talk to the Flaming Lips, who’ve been building a more impressive UFO stage out of supplies found at Home Depot at a cost of a few thousand bucks.)

Zoo TV wasn’t the superior experience only because of technology, though. The early ’90s were the only period in U2’s three-decades-plus career when the band dared to laugh at itself, with Bono trading his messiah complex for irony and the Macphisto alter-ego, and the group suggesting that maybe, just maybe, its desire to save the world was a bit pompous and self-aggrandizing.

Alas, the crusaders were back Saturday, linking “Sunday Bloody Sunday” to Iranian pro-democracy demonstrators, turning “Walk On” into an act of solidarity with Aung San Suu Kyi, the Burmese politician under house arrest, and trotting out Archbishop Desmond Tutu on video to make a plea to end poverty and cure AIDS.

Um, Bono, old chum, many activists cite corporate globalization as the prime culprit responsible for some of the ills just cited. Care to explain how that jibes with you and the band wholeheartedly endorsing Live Nation’s controversial mega-merger with Ticketmaster? On second thought, maybe there was some irony on Saturday.

In between the bounty of new tunes, the band trotted out the expected crowd-pleasers—“Beautiful Day,” “Pride (In the Name of Love),” “Where the Streets Have No Name”—though some of these were truncated or delivered medley-style with awkward bits of covers (“Blackbird,” “Stand By Me,” “Oliver’s Army”), with choppy and unsatisfying results.

As always, the deft rhythm section of drummer Larry Mullen Jr. and bassist Adam Clayton did their best to keep things moving, and the Edge was a deceptively simple one-man orchestra. Meanwhile, Bono posed and preened, emoted and yowled, flogging every millimeter of charisma he possesses. But as someone who’s seen the group on nearly every tour since it first came to the U.S., I never found what I was looking for—that perfect mix of genuine passion and stadium-rock showmanship.

This band just may not be capable of it anymore—which means it may have become the Rolling Stones after all.

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