Because The Endless River is so steeped in Pink Floyd lore, it’s worth going back at least momentarily to the very beginning. Nearly half a century ago, the band started life as a middling blues-rock outfit in London, patterned largely after the Stones albeit with a much smaller repertoire. To fill sets they would extend the songs they did know to great lengths; to justify not rehearsing, they emphasized onstage improvisation. Any technical insufficiencies were masked by sheer volume. Everything read as psychedelic and new, as their still developing chops took the band to places more skilled musicians might bypass altogether. The response was intense: Critics predicted that Floyd would replace the Beatles, and fans lined up around the block for happenings at the UFO Club and Seymour Hall.

As the band progressed, of course, they refined their chops as well as their ambitions—the usual course for DIY musicians (except for Syd Barrett, who quickly absented himself from the scene after spearheading their 1967 debut, The Piper at the Gates of Dawn). Guitarist David Gilmour, brought in to replace Barrett, developed a graceful and patient style that lent Roger Waters’ songs a sense of eloquence and scale. Drummer Nick Mason honed his R&B beats into narcotized motorik timing, and Rick Wright tinkered with synthesizers to add fizzy drama to 1975’s "Shine On You Crazy Diamond", which updated '60s psych to '70s prog and remains his best moment.

All of them—sans Waters, who left the band back in the '80s—figure prominently on The Endless River, a long, predominantly instrumental album that is said to be Pink Floyd’s final cut. All the familiar sounds are here, with each member playing his usual role. The liquid sound of Gilmour’s guitar is immediately recognizable when it enters on the second track, tracing curlicues around the straight lines of Wright’s synths. The song could be "Run Like Hell" in slo-mo or the first half of Wish You Were Here, only with a gentler, more ambient thrust. The title is a wink: "It's What We Do". As regrettable as that album cover may be, it provides a useful metaphor for the relationship between the guitarist and the keyboardist: Gilmour is the punter guiding the boat, Wright is the cloud upon which he floats. Which leaves Mason as the oar, perhaps.

Sadly, Wright died of cancer in 2008, long before The Endless River was even a consideration. To create a swan song for a perennially underrated rock musician, Gilmour and Mason—along with producers Phil Manzanera, Andy Jackson, and Youth—sifted through hours upon hours of sessions from 1994’s The Division Bell, highlighting Wright’s contributions and turning them into new songs. So River is to Wright what Wish You Were Here was to Barrett: a eulogy of sorts, a commemoration of his contributions to the band in particular and to rock in general. Perhaps the band’s most backwards-looking album, it is quintessentially and self-consciously Pink Floyd, for better or for worse. The Endless River is stately, grandiose, and searching, but it is also bloated, pompous, and so conceptually top-heavy it just might fall off the CD rack or crash your computer.

Rather than scrappy young dudes playing to hallucinating fans in the '60s, Pink Floyd have long since become wizened music veterans. As such, they may be too professional and perhaps even too rich to make this music sound like anything other than a luxury item, an option on a sports car or a demonstration CD for home theaters. It’s been decades since we expected grit and glower from the band, but by the time Gilmour starts singing—18 tracks and 46 minutes into the album!—you might suspect that River syncs up perfectly with Cocoon. Not that guys their age can’t make vital music, but the only hint of the passage of time here is their refined chops. And we already knew they could play.

In other words, Floyd’s best and worst impulses are crammed into these 52 minutes. "Sum" and "Skins" are admirably weird, as though the band went as far out as they dared and then took a few more steps. Thanks to the menacingly descending bass line and Mason’s tense drum solo, you can almost see the pulsing laser light show. Those songs elevate the first and second side, promising a more adventurous album than Pink Floyd deliver. The boat sinks beneath the clouds: As The Endless River threatens to live up to its title, the music veers into aimless, repetitive noodling, and the band settle for formless ambience rather than exactingly sculpted songs. There are a few disruptions, such as the Wall-size chords that open "Allons-y (1)" and a monologue by Stephen Hawking on the unfortunately titled "Talkin’ Hawkin'", but such flourishes more often prove embarrassing: Gilad Atzmon’s saxophone turns "Anisina" into an '80s sitcom theme, and the pipe organ on "Autumn '68" plays as a parody of Pink Floyd’s oceanic sound.

Perhaps the sax is obligatory, a nod to Dick Parry’s solos on Wish You Were Here. That would make sense, given the retrospective bend to The Endless River. For the devoted fan, these songs may comprise something like a musical memoir, with references to Wright and Barrett and even Waters ("We bitch and we fight…") as well as to previous songs and albums. Even the title takes inspiration from the final song on The Division Bell, an album which also featured guest vocals by Hawking. That kind of self-referentiality lends much-needed import to what is ultimately a minor entry in the band’s catalog. And there is something warmly reassuring about the familiarity of these sounds, as though Pink Floyd are settling affairs and squaring accounts.

Too often "familiar" curdles into "lazy." As late as The Division Bell, Pink Floyd appeared to be a band constantly looking forward, intent on innovating their own sound if not rock as a genre. As a result, some of their lesser albums managed to build on previous successes, and even that notorious 1987 disaster A Momentary Lapse of Reason has no deficit of ambition or vision. There's something bold in the smaller scope of The Endless River, but it proves to be one of the few Pink Floyd releases that sounds like a step backwards, with nothing new to say and no new frontiers to explore. Of course, if there are no more Pink Floyd albums, then there is no collective future to anticipate, no new sound to build toward. Gilmour, Mason, and the ghost of Wright are closing out a half-century career not with a grand statement, but with a curious ellipsis.