Back in 1999 an American wildlife survey team visited the site of the Chernobyl nuclear disaster to assess the impact of the accident on local flora and fauna. They were astonished by what they saw.
They expected to find blackened scrubland, sick with radiation poisoning. What they actually found was a full-blown wildlife preserve. A thriving ecosystem populated by wolves, eagles, black storks, rodents, wild boar and deer.
That idea, of a hostile place that teems with life, is coming to the PC. STALKER's creators, GSC Gameworld, describe it as a survival FPS. It's a game where your very existence is dependent on your resourcefulness and instinct to take what you must to live.
Tracking down prey; scavenging food; searching for shelter; bandaging your own wounds and relieving your own radiation poisoning are day-to-day activities, alongside working through the missions and exploring the landscape.
Your virtual life requires maintenance. You play a hunter, living off 30-square kilometres of tainted land surrounding Chernobyl.
"Around 2006 something happens within the heart of the Chernobyl reactor. There's a bright light, swiftly followed by massive panic," explains Darren Williams from publisher THQ.
"Everyone thinks there's been a second explosion at the reactor. The military quarantine the entire area in response. But people are curious."
From that point until 2012 (the game's chronological start point) rumours spread about strange humans infesting the zone, alongside pockets of energy and unidentified artefacts.
"A new group of people emerge, the Stalkers, mercenaries who enter the zone to explore and retrieve the artefacts. You play a novice, being nursed back to health by an arms dealer," explains Darren.
When developers talk about AI, they normally like to play it safe and talk about non-specifics. They say enemies will work in packs; that CPU forces will retreat if under fire, and they'll point to the way their infantry uses cover. But they won't explain why.
Why does a creature do the things it does? What's going on under the surface? What is their motivation? STALKER attempts to redress this lack of character. There's a reason for the action.
The wild animals are chasing down food because they're hungry. They look up, take note of you, then wander off. You're of no consequence. You are not a threat. There's an ecosystem at work.
This world is as detailed as we've ever seen. These visuals match, and yes, outclass anything we've seen in those banner games, Half-Life 2 and Doom 3.
That's why STALKER might just be ahead of its time: the huge play area, the constant changes and movement... it's like nothing we've played.