The Roots' Game Theory turns 20, the Def Jam album that changed their course

The Roots released Game Theory in 2006, and The Quietus has marked its 20th year with a reassessment by Angus Batey that treats the record as the turn their whole later career hinges on.

The stakes at the time were high. It was the band's first album for Def Jam, and they had been picked personally by the label's new head, Jay-Z, for whom they had worked as the backing band on his MTV Unplugged appearance and album.

It was also supposed to be the moment they crossed over. Acclaim for the early albums had been capped in 1999 by the Grammy-winning Things Fall Apart, which eventually went platinum though it took a while to reach a millionth sale, and neither the eclectic Phrenology in 2002 nor the leaner The Tipping Point in 2004 had moved them into the mainstream.

Batey traces why the climb was so slow. A purist hip-hop audience treated the band's use of live instruments rather than samples with suspicion, and the group had a habit of writing scathingly, if subtly, about what was wrong with rap. That was true even though Questlove and Black Thought had come up busking around Philadelphia, more literally from the streets than most of their peers.

Game Theory did not fix any of that commercially, and Batey argues it is the reason the band survived the collapse of the recorded music business rather than being buried by it. Twenty years on they are still working: they brought their Roots Picnic festival to the UK for the first time this month, and their first new studio album in over a decade is rumoured to be close.

The anniversary lands in a busy season for hip-hop reappraisals, alongside Outkast's Idlewild at 20 and Frank Ocean's Blonde at 10, while the man who signed them has an HBO series arriving on September 18.