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E3: Left 4 Dead 2

Out of the frying pan, into the fire.

You can usually rely on Valve to do the unexpected, even if the unexpected is exactly what you'd expect any other developer to do. Valve isn't known for its haste in following up successful games, and you might have thought it was high time for more Counter-Strike, never mind Half-Life or Portal. But with Left 4 Dead recently reissued in a Game of the Year Edition and still selling like shotgun shells in a zombie apocalypse, Valve has uncharacteristically decided to strike while the iron is red hot.

The result, to be perfectly honest, is more of an expansion pack than a full-blown sequel, although we can't imagine any of the legion fans of this blistering, definitive co-op shooter will mind in the slightest. Left 4 Dead 2 presents five complete new campaigns starring four new characters, and transposes the action to a poignantly ruined New Orleans. It adds melee weapons, reworked guns and new ammo, and one new boss enemy type. That's your lot.

(Update: No it isn't! Although Erik Johnson was quite matter-of-fact with us about the game's limits, he missed a few things out. His colleague Chet Faliszek has been forthcoming elsewhere, discussing gauntlet moments - where players are thrown through a relentless onslaught of zombies in close quarters, such as on a narrow bridge - and the Wandering Witch, who stumbles around in a daze, making her harder to avoid. There's also a hazmat-wearing basic Infected, limb loss, and unannounced extra boss enemies and a new game mode, while the AI director should have more control over level layouts and weather this time. Apologies for not including these details originally - blame lack of sleep.)

It's easy enough to see Valve's reasoning, however. If it ain't broke, don't go back to the workshop for three years to fix it; iterate fast instead, churn out the content, and feed the rabidly hungry mouths presented by the audience of any hot multiplayer game before they turn away. In a way, it suits the immediacy of Left 4 Dead to be followed up so fast - and the result is every bit as compelling.

The four new survivors are white-suited playboy Nick, tough girl Rochelle, burly Coach and wiry Ellis. I didn't, frankly, dwell on their characters and back-stories, choosing to plunge straight into a run through a campaign called The Parish with three other players that ended ignominiously about half an hour in. Anyway, it's the city that's the star of Left 4 Dead 2. New Orleans' sultry atmosphere and crumbling decadence are captured perfectly through the rubble, brightly lit with washes of hazy, late-afternoon Louisiana sun. It's gorgeous.

The Parish leads you from seedy docks, through veranda-decked French Quarter back-streets, and into manicured parks. We're promised a broad range of other environments from the region (one of them surely has to be the bayou). The game looked considerably better on PC, although the resolution of Valve's ridiculously expansive monitors probably accounted for some of that. Overlaid, directional, on-screen prompts guide you to weapon and ammo pick-ups, and following them introduces the reworked guns - all with an improvised, lashed-together feel, but packing a big kick - and also the melee weapons and incendiary ammo.

Melee weapons are powerful, temporary items - the examples to date are an axe and the famous frying pan from the trailer - that incapacitate your two guns while you hold them, and prove very useful when dealing with the sudden, overwhelming flash-mobs of mauling infected of which our AI director seemed inordinately fond. Incendiary ammo adds a fire effect that can spread from zombie to zombie and is also useful against crowds, but is probably better employed at range, for obvious reasons.

New enemy the Charger made a big impact; bulky, but incredibly fast, this American football-inspired monster will pick a target out of the four of you, run you down and then straightforwardly but powerfully beat you up. Co-op technique with these guys is mostly a matter of keeping a watch for their possible arrival from all quarters - some areas are terrifyingly open - and organising focused fire quickly to take them down. Smokers seemed a little more devious than before, too, lashing their tongues around obstacles like complex pulley systems to keep themselves out of obvious lines of fire.

Otherwise, the relentless pace, unforced co-op dynamics and constant tension and surprise for which Left 4 Dead is justly celebrated are all present and correct. Like its infected hordes, this one's an absolute no-brainer, even if the people making it are very far from that. Read on for an interview with Valve's Erik Johnson to find out why the made it now, why exclusively on 360, and more.