Just how long have we been waiting for this? A four-player co-operative shooter in a city overrun by zombies - a concept so obviously wonderful (and wonderfully obvious) that it could have been plucked from the halls of the very gods.
The initial release of Left 4 Dead will consist of four large campaigns (each spanning five or so maps) which will cover a mile's worth of streets, tunnels, decaying buildings and general urban claustrophobic spaces - all devoid of human life but packed with the Infected. The general rules of play are simple: don't get your noggin nibbled and do your best to escape.
"In one campaign, the Survivors have holed up on the rooftop of an apartment building," explains the game's creator Michael Booth when further details are demanded. "Their food and water supplies have run out, but they've seen a military helicopter making occasional visits to the helipad on the roof of the hospital across the city. They decide to run the gauntlet to the rooftop helipad in the hope of radioing the helicopter and escaping." In between them and the hospital, however, lie 'fast' zombies of the 28 Days Later ilk, boss creatures who can lob cars and puke zombie attractant juice on your team members and not very much ammo at all.
"The overall objective of 'survive and escape' works well because the moment-to-moment experience is very fluid and intense," continues Booth. "Working as a team, rescuing friends from various dangers that flare up, fighting the hordes as well as Infected bosses, finding your way through the sprawling landscape - all of which occurs in unpredictable areas and at unpredictable times. It should all keep players on their toes."
ONE SMART ZOMBIE
Left 4 Dead originally sprouted from (Valve chums) Turtle Rock's work on Counter-Strike bots in Condition Zero. The quality of the bots they created utterly eclipsed that of the finished game, and AI remains at the forefront of their infected plans.
"When you say, 'Our zombies have excellent AI', it sounds a bit odd since most people equate AI with doing clever behaviours and being smart," continues Booth. "However, it also includes things that people take for granted such as knowing how to walk, run, crawl, jump or climb from point A to point B, which can be very complicated. A horde of Infected becomes much less intimidating if they all get stuck on a car in the street..."
And so, coupled with a few nodules of cleverness that let the AI talk to the engine's animation, and ragdolling functions to give zombie horde deaths a mite of the old 'spectacular', your foes will be able to go everywhere you can - and do it worryingly quickly. Or, as Booth indicates: "Whatever an enraged person might do in a similar situation to get to the target of their rage."
HUNTER AND HUNTED
But of course, the zombie plague isn't just made up of undead businessmen and tramps - the Infected come in far more fearsome guises than this. The Hunter, for example, boasts remarkable speed and the ability to leap massive distances - even up walls. The Smoker, meanwhile, has a long tongue capable of plucking a member of your squad right off their feet and out of the sanctuary of the group. Surviving in a zombie-infested town means covering each other's backs and moving in formation, but with creatures like this around it's not going to be easy.
Luckily, there's a way to escape the anxiety of being stalked. If you fancy running around like you're about to miss your bus and are pretty angry about it, you can play the game as a zombie instead. Or, indeed, one of his more powerful counterparts.