When an original member leaves an established band – no matter what the reason – the respectable thing to do is to break up. Too often, though, the band, thinking itself invincible, soldiers on like a staggering amputee, embarrassing itself and its fans with a swift and certain downward spiral into the land of mediocrity and eventual obsolescence. It's one of rock and roll's biggest clichés. The list of bands that have run this painful course is endless. At first critics laugh and then ignore such bands when they fall prey to that slippery slope and fans quickly become turncoats, while the bands themselves suddenly start trading stadium shows for more intimate club tours "to be closer to the real fans." And we all know what that means.

It's a colossal gamble to count your losses and try to forge ahead artistically when you lose an integral member of your band, especially when you're losing a guitarist of the caliber of Graham Coxon. Blur evolved from the sidelines of the trendy Manchester "baggy" scene at the start of the 1990's into one of Britain's finest pop outfits through sheer perseverance and buckets of talent. It may seem extreme at this point, historically, to compare the partnership of Albarn and Coxon to that of Jagger and Richards, Morrissey and Marr, or even Lennon and McCartney, but when the dust settles, Blur's contribution to the musical cannon will endure on that level- at least in England, anyway.

So, Think Tank will be scrutinized more than any Blur album thus far. Whether that's fair or not is beside the point. The fact is it will be, and Blur knows it. Does the band simply rest on its Britpop laurels, churning out a batch of singles for sure-fire chart success? Not even close. Think Tank is Blur's most cerebral, wildly experimental album, ever. Damon Albarn avoids any hint of pub rock in these arty pastiches, allowing his remaining bandmates, Alex James and Dave Rowntree, to step up to the plate and flex their artistic muscles. The result is music that has depth beyond the surface pleasure of a catchy turn of phrase or even a memorable riff. It's music that needs time to sink in- time to wrap itself around your head.

Albarn's work outside of Blur over the past few years has obviously influenced his songwriting. The success of Gorillaz notwithstanding, Albarn is loyal to Blur over anything else. His competitive edge drives him to want Blur to be revered on the level of Radiohead- as an artistic force, and it frustrates him that he has to work harder to achieve that than chart success. But at least it shows that his heart is in the right place. Chart success is fleeting; integrity never fades. His ego-stuffing trip to Africa to play musical diplomat to the natives affected him deeply, and the resulting Mali Music album revealed a breadth of musical instincts that Albarn had never been able to explore in the confines of Blur- until now.

Think Tank is Albarn's drastic reinvention of Blur. He claims it's about politics and love. The former is only hinted at, thankfully, while the latter dominates his pen. "Ambulance" begins with a dark, enveloping groove, replete with horns and smoky keyboards, as Albarn croons in his delicate falsetto "I ain't got nothing to be scared of/'cos I love you." The first single, "Out Of Time" is, perhaps, Albarn's most poignant composition to date. What it lacks in lyrical wonder, it more than makes up for in sincerity of performance. Albarn's soporific voice just shimmers over the quietly plonking acoustic guitar and James' brooding lead bass. It's one of those songs that just grabs you immediately with its delicacy and sullen grace. As a single, it's subtle, but its claws are sharp.

Once "Crazy Beat" kicks in it's obvious why Coxon decided to part ways with his longtime mates. Fatboy Slim's production is soulless and bombastic while Albarn's paean to Bowie-style glam is thin and hackneyed. It's an album low. Ironically, though, the rest of Think Tank is minimal and experimental, which is exactly the direction Coxon tried to steer Blur on its last two albums (despite what one might glean from his slightly embittered claim in the press that Think Tank sounds "underdeveloped and tech-y"). Even the guitar parts should impress Coxon, who always avoided the obvious progression in favor of the diverging melody, and that's exactly what Albarn does here- just with less technical precision and flash.

"Good Song" lives up to the spirit of its terribly uninventive title, as Albarn croaks his lovelorn lyrics over a sparse acoustic backdrop. His dilettantism with electronics never sounds trendy or bandwagonesque, even in its wide-eyed wonder. The world-music backbone of Think Tank melds with the subtle electronics to create a palette not dissimilar to what The Clash was doing twenty years ago, except with Blur, of course, it's a tad less aggressive (particularly without Coxon thrashing away). Furthermore, Think Tank brings to mind army fatigues, desolate tracts, rusty, exposed engines and static by way of the band's careful deconstruction of simple sound effects and musical worlds colliding. It's inherently retro-futuristic in all its calculated inauthenticity, as Albarn lives out his counterculture fantasy cum political subversiveness like a blindingly idealistic college student.

The loose feel of "Brothers And Sisters" would die a painful hippie death if it weren't for the drug-laced lyrical theme and Albarn's ultra-cool, deadpan delivery of every drug he can name. The smoky distance of "Caravan" unfurls in a meandering wave of disjointed, sun-glinted bliss. Blur's youthful brashness finally surfaces on "We've Got A File On You"- a one-minute, explicitly 'British' punk anthem laced with middle-eastern twang (for older fans- it's the album's obligatory "Chinese Bombs"). "Sweet Song" lulls its way into your consciousness with its crystalline melody and light drizzle of piano, and the groove-oriented "Jets", while overlong and repetitive, showcases Alex James' spot-on intuition on the bass.

When Graham Coxon finally does turn up for a song, it's like a blast of white-hot sunshine, which works against the idea that Blur can exist without him, despite everything Think Tank has led you to believe thus far. "Battery In Your Leg" may just seem like another one of Albarn's languid ballads, but Coxon's guitar work splinters through the crescendo, giving the song its urgency and strength. It's the album's most sublimely stunning moment, and it closes Think Tank on stirring note.

Blur has never been a band that stood in one place for too long, and Think Tank proves that with or without Graham Coxon, Blur is still as vital a force as it was nine years ago, when its seminal Parklife album changed the face of British music forever.