Ask a half-dozen U2 fans about No Line on the Horizon and you’ll get three dozen different opinions—all of them forceful. Released in 2009 after countless delays, the group’s 12th studio album proved to be immediately divisive. Even now, years later, it’s one of the most-debated entries in U2’s decades-spanning catalog, with listeners still trying to suss out what to make of this late-period oddity: Did the band members push themselves in the wrong direction while making No Line on the Horizon—or did they not push themselves enough? And is the resulting album a respectable near-miss, an overlooked treasure, or a full-on artistic flop? One thing’s for sure: No Line on the Horizon had the most painful and protracted gestation period of any U2 album—though not without good reason. The back-to-back successes of 2000’s All That You Can’t Leave Behind and 2004’s How to Dismantle an Atomic Bomb had restored U2’s post-Pop mojo, and yielded several can’t-miss new-millennium rock anthems. But to the band members, the idea of going back into the studio and trying to recreate the magic of something like “Beautiful Day” or “Vertigo” was likely a daunting prospect—not to mention an uninspiring one. After all, this is the group that, years earlier, had abandoned the anthem-packed, arena-filling sound of The Joshua Tree, replacing it with the glittery leisure-suit electro-kitsch of Achtung Baby— to this day, one of the riskiest, and most successful, rock ’n’ roll reversals of all time. For Bono, the Edge, Larry Mullen Jr., and Adam Clayton, change was a semi-constant necessity—albeit an uneasy one. Still, no one expected the making of No Line on the Horizon to take almost five years, as the group chased one idea after the next. Because this is U2—a group with the chattiest lead singer of all time—fans spent nearly half a decade getting fitful status reports via the press: At first, the record was going to be a mighty team-up between U2 and super-producer Rick Rubin. When that collaboration failed to yield an album, word got around that U2 was back with Daniel Lanois and Brian Eno, the duo behind such hits as The Unforgettable Fire and The Joshua Tree. At some point, it became clear the band was also spending time in the studio with Steve Lillywhite, the group’s on-again, off-again producer since the early 1980s. Multiple recording sessions with multiple producers in multiple cities—all with multiple promises that the band members were exploring new sounds. And yet, for years—no album on the horizon. Then, in early 2009, U2 appeared at the Grammy Awards, opening the show with a new single: “Get On Your Boots,” a glammy riff on Dylan’s “Subterranean Homesick Blues,” featuring so many fast-paced Bono bon mots, you almost needed a bottom-screen ticker to keep track of them all. It was a tough watch—the sight (and sound) of a band doubling-down on one of the weakest tracks from its newest album. And while No Line on the Horizon would go on to sell millions of copies, and eventually inspired a gazillions-grossing worldwide tour, the decision to make “Get On Your Boots” the lead-off single killed the album before it even had a chance. Which is a shame, because No Line on the Horizon has its share of solid tunes. And while they’re not as boundary-pushing as fans may have hoped, they do find U2 trying to get past the big-riff mindset that had hampered the group at times in the early 2000s. The title track, which the band co-wrote with Lanois and Eno, is a gentle epic, with cryptic guitars, careening synths, and some of the most subtly daring drumming of Mullen Jr.’s career. “Magnificent,” meanwhile, feels perched somewhere between the desperate uplift of The Unforgettable Fire and the glossy future-rock of Achtung Baby. Even when the tracks feel more like soundscapes than songs—as with the haunting “FEZ — Being Born”—there’s a genuine sense that these guys are, for the first time in a while, truly trying to push themselves. But in the middle of all this? “Get On Your Boots.” Not to mention the even more ridiculous “I’ll Go Crazy If I Don’t Go Crazy Tonight”—a perfectly forgivable dumb-fun song, but one that feels like it was included here in a desperate bid for an easy hit single. That never happened—and No Line on the Horizon, despite its multi-platinum status, failed in its mission to reinvent U2 for the 2010s. The band members would soon retreat to even more familiar sounds. For U2 diehards, No Line on the Horizon will forever be akin to 1997’s similarly calamitous Pop: A record that could have marked an exciting new era for U2, and that many fans still turn to from time to time, hoping that, at some point, they’ll finally be able to locate the lost masterpiece hidden underneath. But, for the most part, they still haven’t found what they’re looking for.