In the years after the release of OK Computer, popular music went through another stylistic transition, with the early-’90s moment when weird alt culture could share a stage with Céline Dion giving way to nu-metal, teen-pop, and the broadly appealing politesse of “American Idol.” Total sales for the global recording industry topped out in 1999, at nearly $29 billion, and then tumbled for more than a decade. Print journalism, which had thrown all of its weight behind OK Computer, saw its business collapse around the same time and for similar reasons.

Pundits appear to have been right that OK Computer was the last of a particular kind of album, one made by guitar-centered bands interested in creating a full-length artistic statement that could achieve mainstream popularity while advancing, but not departing from, the “rock” tradition. But OK Computer also pointed toward a post-rock reality; on 2000’s Kid A, the band made the break explicit, sidelining live instrumentation in favor of a dive into oblique electronic music. Though other rock groups had dabbled in techno flourishes before, Kid A once again sounded like the future. And with that album, all but the most diehard rockists finally had to admit the obvious: The classic art-pop album, as embodied by OK Computer or Dark Side of the Moon, didn’t depend on guitars at all. It’s no coincidence that, while nearly all of Radiohead’s records have been well-received, Kid A is the only one that typically rivals OK Computer in the best-album-ever sweepstakes.

Rock lost what remained of its commercial and cultural centrality in the years that followed. Meanwhile, the most groundbreaking music was being made by sleekly cosmopolitan hip-hop, R&B, and pop producers like Timbaland and the Neptunes. The burgeoning critical consensus that chart titans could be as significant as rock auteurs earned a name: poptimism.

There were still great art-pop albums, but, increasingly, they weren’t necessarily rock albums. Across the last 20 years, monumental rap, R&B, and pop records like D’Angelo’s Voodoo, Kanye West’s My Beautiful Dark Twisted Fantasy, and Beyoncé’s Lemonade have filled the void of full-length statements with both artistic seriousness and mass appeal that was formerly largely occupied by guitar bands. At the same time, the ranks of professional music writers are becoming more diverse, which has no doubt also played a part in ending rock’s disproportionate stranglehold on year-end lists.

Over the last few years, the traditional album has faced new problems. In 2014, global record industry revenues hit bottom; even as they’re now crawling back up thanks to widespread streaming, it’s still not an environment for high-risk bets on albums of questionable marketability. But that hasn’t stopped some of music’s biggest names from taking huge artistic plunges—in a way, it seems as though the lowered monetary stakes have caused people like Rihanna and Beyoncé to let their inner-art-student run free. And last year, Kanye West’s The Life of Pablo made the definition of any specific album itself a form of artistic expression, through a number of post-release tweaks. The shape of the album to come remains to be envisioned.