First up though, the facts. 21 signifies 21 years since the release of first album Leisure. It contains all seven proper albums – Leisure, Modern Life Is Rubbish, Parklife, The Great Escape, Blur, 13 and Think Tank – now in long overdue deluxe editions with additional B-sides and odds and sods from each period. There's another four discs containing even rarer stuff dug out of boxes from the band members' lofts. There are three DVDs too. Showtime is a live show from Alexandra Palace at the end of 1994; there's a previously unreleased Singles Night performance from 1999 where their played all their – hey – singles in order. The third DVD collects everything from a homemade video from when they were called Seymour to daft TV bits and rare videos. Oh, and there's also a seven inch of the Seymour track 'Superman', recorded at one of their very first gigs. That's over 18 hours of music, nearly five hours of visuals and basically as much Blur as one can probably stomach in a whole sitting without being whisked away for being insane.

Mop of hair and a slightly more psychedelic take on the even-then knackered-looking baggy bandwagon, the thing that helped elevate Damon Albarn, Graham Coxon, Alex James and Dave Rowntree above the likes of My Jealous God was 'She's So High'. A shimmering, chiming, woozy piece of special, free of a dance element, and enough to pique interest in going further. The B-side 'I Know' is much more of its time now, but it's clear to see that the band that would claim they killed baggy only did so because it didn't really offer them the opportunity to be 'them'. Tucked away on the other formats were 'Down' and a version of 'Sing'. These seemed more like it. You could understand why Melody Maker were digging them.

Leisure was perhaps too eager-puppy to be a slightly weird pop album, more in the cavalier spirit that had managed to take The Teardrop Explodes to the top. They'd already shown that they were capable of channelling Syd Barret and Ogden's-era Small Faces on B-sides such as 'Inertia' and 'Mr Briggs', so the likes of 'High Cool' seem written to get them on to Saturday morning TV. However, within Leisure lurked the aforementioned 'Sing', plus 'Birthday' and 'Wear Me Down' hint at a future beyond waving chicken heads around.

By the time the band toured Leisure, they were beginning their set with a frenzied piece of marvellousness entitled 'Popscene' which was far punkier and spikier than anything before and hinted at a life beyond a damp debut. It was having failed to crack America and a shit of a manager that left them on their uppers and at their hungriest. When they began recording Modern Life Is Rubbish, they were hovering around the entrance to the dumper and looking on as the then thrillingly new 'Best Band in Britain' Suede came along and cut through the post-grunge malaise.

A combination of all the finest points of guitar-yore combined with a leap in songwriting skill, Modern Life Is Rubbish basically invented Britpop. Alongside 'For Tomorrow' and 'Chemical World', there was 'Oily Water', 'Blue Jeans' and 'Pressure On Julian'. That 'Popscene' wasn't on the album is a tragedy, but disc two retrospectively restores that - and it is there where you'll find the utterly superb 'Young & Lovely', 'Badgeman Brown' and 'Into Another', alongside the very worst cover version of 'Maggie May' your ears may ever hear.

Parklife continued the streak of songwriting quality, and was the band's 'imperial phase'. For an album that was seemingly everywhere in 1994 (well, until at least the release of Oasis' Definitely Maybe) you can still listen to it now and see why it made them enormous. They'd tackle disco ('Girls & Boys') and chanson ('To The End'), and in 'This Is A Low' and 'End Of A Century' they'd pen two of the great songs of the era. Extras-wise, you could begin to hear the quality of the B-sides dip somewhat – 'People in Europe' and the lounge-y pisstakes of 'Beard' and 'Supa Shoppa' aside – 'Rednecks' was piss-poor and certainly throwing three versions of it into this set doesn't alter that.

Having arrived at last, they wasted no time in starting The Great Escape. Recorded during brief sessions when they weren't collecting awards for Parklife, it suffers slightly from observational fatigue. At its best – 'He Thought Of Cars', 'The Universal', 'Yuko & Hiro' – it was genuinely touching, but 'Mr Robinson's Quango' seemed like a rehash of themes touched on in the superior 'Tracy Jacks', and despite finally giving them their first No.1, 'Country House' is just horrible.

By 1997's Blur, it's a different story. Free from what was being referred to as 'the Life trilogy' and reinvigorated by turning up the guitars and being less specific lyrically, it helped them break America with the likes of 'Song 2', and 'Beetlebum' gave them their next No.1. Also, they'd got their mojo back B-side wise, with 'Get Out Of Cities', 'Swallows In The Heatwave' and 'Bustin' & Dronin'. Even better is 1999's 13, where tunes stretch out, snap back and go a bit cosmic in general. They were heartbroken on 'Tender' and 'No Distance Left To Run', genuinely far out on 'Trimm Trabb' and 'Caramel', and completely mental on 'Bugman'. However, at this point live tracks and remixes start to fill out the extras. It would be interesting to hear a bit more of the discarded stuff from that period, the bits that hadn't been Pro-Tooled to buggery. Maybe Blur 25 will address that.

2003's Think Tank is the last of the catalogue, and though largely Graham-less, shows off a broader musical palette than previous work. Coxon had been asked to leave the band as recording began, although he does feature on 'Battery In Your Leg', which alongside 'Out Of Time' is a highlight of the set. But by now the band were seen almost superfluous to Damon's needs, as he was enjoying much bigger success with Gorillaz, released Mali Music and co-founded the Honest Jon's label.

Behind the albums, their hits and their B-sides, highlights are present all over the place: the wonky funk of 'Music Is My Radar'; fan club Christmas treat 'The Wassailing Song' sounding a lot cleaner than my knackered seven inch; the backBackBACK of 'Fools Day' and the possible "we're off" of gorgeous new song 'Under The Westway'. There are collaborations with Marianne Faithfull ('Kissin' Time') and Francoise Hardy ('To The End (La Comedie)'), and yob techno on previously hidden track 'Me White Noise'. It's nearly all there. Had the package decided to throw in the DVD of Starshaped, then it really would be the greatest box set ever.

21 is staggering on a variety of levels. Everything here is supplied to give you the full Blur experience. From the maddening to the imperial, from the feuds and heartbreaks to the extraordinary results, such things drove them on to. There'll never be another band like them. And if this is really it and they leave Blur to the history books, then it's a perfect way to remember this unique, occasionally annoying, but genuinely quite amazing band.