Step back from the hullabaloo surrounding the scale of the National Galleries of Scotland's Generation project - a country-wide survey of 25 years of art, featuring the work of over 100 artists in 60 venues - and it's clear that it's first and foremost a celebration of success.

Even if that wasn't already implicit in the stellar names represented, it's made explicit in the introduction to one of the two books published to mark this weekend's opening of Generation's flagship show, a triple whammy of art spread across three of the capital's four major galleries. Generation, it begins, is a "landmark event" and "one of the most ambitious celebrations of contemporary art ever held by a single nation". It has been inspired, it goes on to say, by the fact that Scotland has developed "an international reputation as a distinguished centre for contemporary art" and produced a "disproportionately high number of award-winning artists."

It's all true. Another way to put it is this: chuck a stick in the Scottish National Gallery Of Modern Art this week and you'll hit a Turner Prize winner who was either born here, trained here or (by dint of the first or the second) lives and works here.

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Generation: 25 Years Of Contemporary Art In Scotland takes up all of SNG's Modern One and the Scottish National Gallery, and spills over into the Scottish National Portrait Gallery where 2012 Turner nominee Luke Fowler is showing a video work. Modern One doesn't have all the big beasts but with art ranged over two floors and connecting corridors, it is the show's epicentre.

Thematically it's a mixed bag, as you would expect. Some artists reflect on Scotland and the Scots, some are far more internationalist in outlook or more personal.

Kate Davis, for instance, presents large, almost photorealist-style drawings of crumpled postcards of paintings of female figures, a feminist critique of how men view women. Claire Barclay's massive sculptural piece Trappings, made specially for this show, gives an alternate view of the domestic by draping what look like printed quilts over a wooden frame wound round with yarn.

Some, like Graham Fagen and Torsten Lauschmann, reveal an interest in theatre and staging and use those interests to ask questions about reality and illusion. Others, such as Lucy McKenzie, invoke ideas drawn from classical art - a trompe-l'oeil painting fixed to the ceiling in her room turns it into a baroque bedchamber or maybe a tourist-choked Roman church - or they simply put pen to paper to create packed, picaresque streetscapes (Charles Avery) or beautifully precise abstract designs (Richard Wright, a Turner Prize winner in 2009). Henry Coombes, whose wonderful film The Bedfords is one of the must-see exhibits, examines class with a mixture of whimsy and fancy, while Toby Paterson's fascination is architecture, urban space and the built environment.

Each room brings its own very particular treasures. In some of them are artists who deserve to be better known - Julie Roberts, for example, whose paintings of de-peopled straitjackets, operating tables and mortuary slabs are bold, vivid and troubling - or who soon will be, such as Alex Dordoy. Still in his twenties, he shows found objects alongside three flat, almost diagrammatic paintings of a catamaran rendered at dawn, dusk and at night.

Of course the idea of looking at a quarter of a century's worth of Scottish art is about more than just curatorial neatness, and it's worth bearing that in mind as you wander the halls. There is a point to the number. It was around 25 years ago, for instance, that Callum Innes began moving away from figurative painting into the world of block abstracts he still inhabits and in which he has carved his reputation. It was around 25 years ago that Ross Sinclair was completing his studies on Glasgow School of Art's now-celebrated Environmental Art course, the engine that has driven much of Scotland's conceptual art since. And it was around then that Alison Watt and Douglas Gordon were graduating from the same establishment and embarking on art careers which within one year and seven years respectively had brought a commission to paint the Queen Mother and a Turner Prize win. That second honour came thanks to Gordon's 1993 work 24 Hour Psycho, a slowed-down version of Alfred Hitchcock's Psycho. It sits in Modern One's main hall, downstairs from a light-flooded room in which Watt shows a series of her enigmatic paintings.

Sinclair, meanwhile, has recreated his much-loved Real Life Rocky Mountain installation in which he is also centrepiece and master of ceremonies. Basically it's a confection of fake grass, fake boulders, stuffed animals, a hut, some electric guitars and, in this latest incarnation, a video monitor showing Sinclair with hair (dreadlocks, no less) performing the same piece at some point in his (and its) past. If he's still doing it in another 25 years' time, it will become even more poignant. But with its explorations of kitsch and national identity and its use of Sinclair and his body as a participant - he always performs in the same green tartan shorts, stripped to the waist so as to reveal the Real Life tattoo across his back - it reveals a man well ahead of the artistic curve. Songs by Orange Juice and Belle And Sebastian get a run-out at the press view, and Sinclair will be returning from time to time to perform more of the same in situ. Do take the kids.

But the most important reason why 25 is a magic number is to be found at the Scottish National Gallery. If there's a ghost at this feast of Scottish art (though his would be a likeable shade) it's Steven Campbell, who died in 2007, aged 54. In the gallery's first room is his 1990 work On Form And Fiction, seminal because it was shown at the CCA in Glasgow in the same year as the city became European City of Culture and because it takes the figurative art of the so-called New Glasgow Boys of the 1980s - Campbell himself, Stephen Conroy, Peter Howson, Adrian Wiszniewski and Ken Currie - and catapults it into the conceptual 1990s, anticipating what was to come.

The work consists of eight, large framed paintings mounted on hardboard onto which are stapled a series of paintings on paper, so many that they completely cover the walls. Some show images that look as if they're illustrations torn from a novel by John Buchan, others show scenes which are picaresque, allusive, sombre or unfathomably mysterious. There are two benches - borrowed from Kelvingrove Art Gallery - and a table containing an old Grundig reel-to-reel tape recorder. It plays Serge Gainsbourg and Jane Birkin's Je T'Aime, Moi Non Plus on a loop. Amazingly, this is the first time it has been shown since it finished touring in 1990.

Next to the Campell room are six cool abstracts by Callum Innes, from the Exposed Paintings series he began in 1994 and which continues today. Given the 20-year span they cover - the most recent, Phthalocyanine Blue, was completed this year - they have a commendable unity of tone. Elsewhere there's a video piece by Rosalind Nashashibi, a sculptural installation by Karla Black and rooms given over to work by Christine Borland (Turner Prize nominated in 1997, the year of the all-women shortlist) and Martin Boyce (Turner Prize winner in 2011).

Both those artists inhabit the chewier end of the spectrum: Borland shows L'Homme Double, a conceptual installation from 1997 comprising six sculptural heads of Nazi war criminal Josef Mengele which Borland "commissioned" from six separate artists who were supplied with the same information but produced markedly different works. Boyce, meanwhile, shows a 2002 sculptural work, Our Love Is Like The Flowers, The Rain, The Sea And The Hours, made up of neon strip lights, chain-link fencing and stylised litter bins - a facsimile of the urban parks he frequented as a child, filtered through the prism of his artist's interest in Modernism and design. It's big and dark and ghostly.

If Borland and Boyce can be characterised as the exhibition's brain and Campbell the seed or the heart, then David Shrigley is surely the funny bone. He presents a room in the Scottish National Gallery decked out with monochrome woodprints (one says simply "Exhibition") and 10 pairs of huge, glossy, black ceramic boots which are mounted on plinths of various heights. Imagine an S&M boutique rendered in plasticine for a Wallace And Gromit film and you're part way there. It's a reminder that alongside gravity in art, there is always a place for levity.

More than a snapshot, Generation is a definitive group portrait. It's also a brave and confident curatorial endeavour which acclaims the work of those artists born in the 1960s and 1970s and attempts to etch into the critical record the names that will really matter in the decades to come. Mind you, when faced with a class as talented as this one, perhaps it's deciding who not to include that requires the courage. But I imagine there's already a Generation@30 show planned which will take care of any oversights.

Generation: 25 Years Of Contemporary Art In Scotland is at the Scottish National Gallery of Modern Art (until January 25 2015), the Scottish National Gallery (until November 2) and the Scottish National Portrait Gallery (until November 2). For other venues across Scotland participating in Generation, see Next week, Phil Miller reviews the Generation shows opening in Glasgow.