Foo Fighters have now been Dave Grohl’s chief concern for 20 years. The first 10 were spent minting the band’s platinum-plated modern-rock sound, and the subsequent decade was spent trying to remold it… only to have it settle back into its predictable color and shape. Indeed, it’s hard to distinguish one Foo Fighters album from another, since they all draw from the same well of arena-punk fist-pumpers, gentle comedown ballads, and arm-swaying sing-alongs that fall somewhere in between; as their Greatest Hits compilation made all too clear, a Foos song from 2007 sounds an awful lot like one from 1997. To his credit, Grohl seems well aware of the fine line between being unerringly consistent and relentlessly formulaic, and has tried to provide each new record with a fresh narrative. But these strategies have essentially amounted to hanging different frames around an unchanging picture—like a double-album opus that simply segregated the Foos’ habitual whispers and screams, or a back-to-the-garage throwback seemingly designed for garages big enough to house private jets.

That said, Grohl's latest plan to drum up interest for a new record could be his most ingenious: make the most elaborate, expensive EPK in music history and have HBO distribute it. Sonic Highways is the name of both the Foos’ eighth record and an accompanying, eight-part TV series documenting its ambitious, cross-country production process, with the band (alongside Butch Vig) recording each of its eight songs in a different city. It effectively blows up the concept of Grohl’s 2013 film, Sound City, to a national scale: visit a renowned musical mecca, speak to the legends that put it on the map, and hope some of their mojo rubs off onto new recordings.

As a documentary, the Sonic Highways series takes full advantage of Grohl’s unique status as a punk-spawned celebrity to deftly intertwine mainstream and underground rock histories. For instance, so far we've seen how Chicago-blues icons like Buddy Guy and noisy nihilists like Big Black were both fueled by the same impoverished necessity, or how hardcore pioneers Minor Threat and go-go greats Trouble Funk shone a light on the Washington that lurks in the shadow of Capitol Hill. As a promotional film for a new Foo Fighters album, however, it makes you wonder why its trailblazing subjects’ transgressive influence didn’t seep into the sound of final product.

Though it's all relative, Sonic Highways is the most adventurous Foo Fighters album to date, but it bends their trusty template in ways that bear little relation to the project’s underlying musical-history-tour gambit. (It’s not like hanging out with Bad Brains inspired a sharp left turn into light-speed D.C. hardcore, or digging up Roky Erickson’s roots in Austin has introduced sunbaked psychedelia into the mix.) Rather, at eight tracks and 42 minutes, Sonic Highways is paradoxically the Foos’ leanest record while boasting their most sprawling compositions, taking a more scenic route to their usual destinations.

Where most Foo Fighters songs have shown their hand by the first chorus, the highlights here gradually build up in step-like fashion: “Something From Nothing” may boast a typically teeth-clenching Foos climax, but it rides a surprisingly funky (if uncannily Dio-esque) organ groove to get there; “What Did I Do?/God As My Witness” stays well within Grohl’s power-pop pocket, but its stop-start/two-part structure suggests Big Star’s “Back of a Car” given a musical-theater makeover. And even songs that travel a straight-and-narrow path have a welcome sense of patience about them, revealing new melodic nuances along the way (like on the dreamy jangle-pop of “Subterranean”) or, in the case of "Congregation", unexpected dynamic shifts: what starts off as a standard-issue, cruise-controlled rocker in the “Learn to Fly”/“Times Like These” mold acquires a more intense energy, thanks to an extended soul-stomping breakdown buoyed by Zac Brown’s finger-picking.

But given the great logistical effort that went into the album’s creation—and the fanboy reverence Grohl exhibits toward his interview subjects on each "Sonic Highways" episode—it’s unfortunate that the regional essence of a given a song is barely perceptible without the televised exposition. Beyond illustrating that upbeat pop-punk is an odd forum for a discussion of the '68 D.C. race riots (see: “The Feast and the Famine"), the album boasts a bounty of special-guest ambassadors who are given little room to assert their personalities amid the Foos’ chromatic crunch: the New Orleans Preservation Jazz Band doesn’t have much to do on “In the Clear” but chirp up its mid-tempo riff; Joe Walsh’s bluesy fills get lost in the fast lane of “Outside”; and good luck parsing out the presence of Joan Jett on “I Am a River”, a gaudy Macy’s Day Parade of a power ballad that, just when you think can’t get any more overblown, piles on a false ending and string-section finale. The composite cityscape seen on Sonic Highways’ front cover proves to be all-too emblematic of the album’s overall sound: a hodgepodge of aesthetic signifiers that get swallowed up into a monolithic whole.

Watching "Sonic Highways", you get the sense that the real purpose of the whole endeavor wasn’t so much to reinterpret the musical traditions of a given city as simply broaden Grohl’s lyrical perspective beyond his usual relationship-focussed ruminations and self-help affirmations. In some of the episodes that have aired so far, we see a shot of Grohl sitting down after completing his interviews to write a song based on all the local lore he’s absorbed; the episodes then conclude with the Foos performing the resultant track, as the lyrics—loaded with knowing references to “muddy water,” “the 13th floor,” and “bluebirds”—are splashed across the screen practically begging for I-see-what-you-did-there acknowledgement. Ironically, in trying to tap into the mystique of America’s most storied cities, Foo Fighters completely demystify their own creative process, effectively turning the Sonic Highways project into a glorified homework assignment—educational, perhaps, but laboriously procedural.