There's an iconic SF moment right at the start of Iain Banks' latest novel: the mechanical preservation of a severed head. Admittedly, it's the head of an enemy that's been inverted and used as a punchbag by the demonic protagonist of the piece, an arch sadist with a Swiss army knife for a cock, but it's an iconic concept nonetheless: the continued survival of the mind/personality beyond the death of the body. From Futurama's jar celebrities to Dennis Potter's Cold Lazarus, this form of cheating the Reaper prevails over other conjectures such as gene therapy and wonder drugs. There's something wonderful and simultaneously horrific about the notion of continuing life without your body; repulsive and, potentially, a cause for hope - especially among the younger fans of Banks' more speculative work.

For now, however, the anticipation of "most eagerly awaited science fiction novel of the decade" - as the promotional tag line of the reviewer's proof assures us - is over. It's here. And while Banks may have curbed his prestigious output in recent years, he hasn't lost his ability to seduce his fans.

His work combines very personal tales and against intergalactic backdrops filled with strange new life and unnatural oddity. It's a winning amalgam for the loyal, but not one that'll earn any new faces at the signings. If you're fresh to Banks' sci-fi output, you'll struggle with The Algebraist.

The opening is fragmented and contains an extended roll-call of characters with convoluted names, all tied into a plot that takes a good 100 pages to get rolling. Not only that, but one of the strongest characters in the opening section is subsequently consigned to the occasional walk-on, and just about every transparent surface appears to be made of diamond. There are flaws; the good news is that once the leviathan of a plot finally gets up to speed, you forget about the problematic opener and realise that only a beach full of tank stoppers is ever going to bring it to a halt.

Although this isn't one of Banks' Culture novels - he tends to deviate from his utopia in alternate pieces of SF - The Algebraist sports a much more expansive feel than the closed worlds of, say, Feersum Engine or Inversions. And, refreshingly, it's set within a section of the galaxy where Earth features as a planet. Previously, the only references to our own spiral arm of the galaxy have been fleeting - see State of the Art and precious little else.

So, instead of the usual AI minds that inhabit the drones and ships of the author's Cultural output, we find a society very much in the shadow of its machine-dependant past. AIs are despised and hunted down like medieval witches, while the alien powers-that-be hold tight control over an elite body of ruling families, or Septs.

Against this politicised backdrop, we join one Fassin Taak - a human slow seer engaged in the xenopological examination of a race of giants called The Dwellers.

Here, among the clouds of Nasqueron, Banks once again leaves his mark. With Herbert and Aldiss, we've encountered compelling worlds of inspirational vegetation and global aridity. Banks offers us something entirely unfamiliar, at once challenging and alluring. Here, among the vertiginous altitudes and stormheads of this transient world, we discover cloud cities, regattas held across jet streams and a form of childcare that'd have the NSPCC forming an expeditionary force. It's a harsh, weird and seductive milieu, and meticulously constructed. However, its descriptive weight acts like a thematic gravity well, foreshortening all other plot strands and never allowing them to reach escape velocity. This may well be Bank's longest book to date, but I would happily settle in for another 200 to 500 words if only he'd allowed the sub-plot to blossom.

Fassin, as protagonist, obviously dodges this narrative suppression. His story starts as part coming-of-age biography, part political thriller, but soon develops into a galaxy-wide quest for the ultimate weapon to use against a hostile invading force led by the aforementioned prehensile prick-wielding über-villain. And, unlike other more active members of Banks' canonical entourage, Fassin's adventure into this hostile environment is governed by non-violent investigation. As a result, the author indulges his scientific bent by including big ideas and gob-smacking set pieces. Principal among these is the idea of 'The Truth', an adaptation of Edward Fredkin's digital physics, in which all manifest phenomena can be explained as units of information. We are, in effect, living within a vast computer programme called The Universe. Where Banks takes this theory, though, is innovative. Fredkin's 'Truth' transmutes into a futuristic and personal form of religion. The only doctrine of this new church is that everyone should be persuaded to accept the insubstantial nature of reality. Only by doing this can the programme ever be concluded. All beautiful, bizarre and far-reaching stuff, but never enough to cramp Banks' playfulness. Amid nods to genre heritage (with subtle references to Swift's Lilliput and Wells' Time Machine), there appear some great subversive moments - like the brilliant sex scene in which each caress acts like an encoded form of text messaging, complete with SMS-styled syntax... Or how about a warped encounter with a space-faring race that does nothing but collect the corpses of those killed in the vacuum? You can almost sense the sheer pleasure in creating such oddities, and it easily translates into appreciation by the reader. So all the boxes ticked and another best-seller guaranteed to be read unashamedly across the country? Yes, thanks to Bank's weight as a literary force these days, much like the gas giant Nasqueron itself; but not as a result of The Algebraist triumphing as a work of speculative fiction. There's a point where Fassin's quest grinds, momentarily, to a halt, leading him to believe that all his journey holds is "more names to deal with, more places to take in, another damn step along the way." It'd be unfair to say that this sums up all that's problematic with the book, but there is an element of it which will strike even the most hardened fan. The result? A hiatus in that all-important suspension of disbelief.

Whatever its initial failings, when the call to adventure finally kicks in, it comes on like an dragster as Banks, once again, transforms reading into devouring. And with a fan-base as large as his, that's all he ever needs to do to secure himself a place in the top 30. I only hope that the next sci-fi instalment sees a return to the form seen in Look To Windward, and that his laurels remain atop his bearded head - even when it is stuffed in a jar.