This preview is arriving twenty minutes late, because the rigid demo schedule for Modern Warfare 2 was thrown into chaos earlier today when Verne Troyer arrived unexpectedly and was granted an extensive private screening. In this way, at least, Modern Warfare is the Mini-Me of E3: a bona fide showstopper. Every mention of it in the aisles and display areas of the LA Convention Centre is followed by a deferential pause, and other games - even fairly important ones - are often found struggling to get out of its way. Everyone feels a little nervous in the presence of real success, and Infinity Ward's game managed to be one of the genuine stars of a Microsoft press briefing that also included appearances by The Beatles, Steven Spielberg and a hard-coded science-bending Pinocchio.

It might have been safe by now to trade on reputation alone, but Modern Warfare 2's demo has the elegance, intelligence and poise - not to mention the sense of streamlined chaos - that only comes from hard work. Its snowy mountaintops and blizzard-swept bases dazzle at 1080p and 60fps, but an extended preview behind closed doors suggests that the real standout element is the way Infinity Ward's game tugs you along as it slips invisibly from one encounter to the next, varying the approach, restacking the odds, and changing the rules so confidently you hardly notice it.

We start with a touch of isolated spectacle, perched on an ice ledge high above a snowy ravine, on a mission to infiltrate an enemy installation. Our guide is Captain MacTavish, gruff and experienced, his days of taking orders from somebody called Gaz and suffering under strange nicknames long behind him. He's the teacher now, and the player is, once again, cast in the role of eternal student, but what follows is no simple replay of the last game's irradiated saunter through Prypiat.

Climbing an ice wall to the base above is a chance to study the finer detailing, as tiny cracks skitter outwards from the strikes of your picks, frost gathers in MacTavish's beard and the wind whips constantly at the cuffs of your coat. It's also an opportunity for the developer to indulge in a little light scripting, with sudden jet flybys dislodging ice and stone from above, and a daredevil leap that ends up with a - predictable, yet no less effective - last-second rescue.

From there, with the mountain behind you, Infinity Ward offers an unhurried lesson in stealth, as you calmly headshot your way through the outskirts of a base, with a persistent drip-feed of advice and encouragement from your mentor and no need for gauges to tell you how visible you are or alarms to alert you if you're spotted. Once inside the base, a blizzard descends, and you're free to move through the low visibility cloud, taking people out - or fatally stumbling into them - from much closer up.

Tension comes next, as mines are placed and files are downloaded, all while patrols tramp past mere inches away. There's a delicious sense of inevitability as you wait for things to go wrong. They do, of course, and after an understated aircraft hangar standoff between MacTavish and a dozen enemy soldiers, in which you have a chance to provide cover fire, Infinity Ward makes the timely switch from quiet to commotion as gunfire erupts, and the slow, teasing progression of kill-shots and incremental advances gives way to a headlong guided rumble that fills the sky with smoke and the sound of gunfire.

It's here above everywhere else that Infinity Ward really sets itself apart from a lot of its competition, driving you forward through something that really feels like chaos, throwing you past smart combinations of geometry and enemy emplacements as you fight back out of the military installation, the previously windswept calm replaced with ricochets and blood, the jets that rose out of the mist a few minutes ago reduced to burning rubble as attackers take cover behind wheel wells. All the while, whether they're guiding your eye with a distant explosion or directing you with alarm sirens and screams, the developers have proved themselves masters of the linear shooter.

After that, the ensuing snowmobile chase across the mountains is almost unnecessary, but the game never breaks a sweat or drops a frame as you blast off downhill, taking out enemies from all angles, and ducking falling trees, while MacTavish hijacks his own ride with a single swing of his ice pick. Suddenly, a tense, confined game is thrown wide open, with slopes rolling as far as the eye can see, and the pace changing from a thoughtful trek from one advantageous position to the next, to an all-out scramble for the safety of your waiting helicopter. It feels like a rollercoaster, but the truth is, even back there when Modern Warfare 2 was at its most stately, you were already on one.

The snowmobile sequence is apparently made possible by the team's new texture-streaming technology, which allows for larger environments without a jarring loss of detail, and, despite the speed of the delivery, this remains a very detailed game. From the tiny icicles hanging from window ledges, to the snow building up on the flapping tarpaulins that cover the base's crates, there's something to see everywhere you look, and the animation's as strong as the environment: MacTavish's practiced swipe of the ice pick, or the manner in which he readjusts his ropes after a long climb, are entirely natural, and character and weapon models boast both detailed mapping and normal mapping.

With style to spare and a uniquely confident approach to varying pace, then, Modern Warfare 2 is looking as fearsome a contender for the Christmas top spot as you might expect. And the really scary thing is this: nobody's even mentioned multiplayer yet