S.T.A.L.K.E.R.: Shadow of Chernobyl has always been an overly ambitious game, which is probably why it has arrived several years later than originally expected. The game's goal is to create a virtual world with an ecology all its own and then place you in the middle of it. That's something that's rarely been attempted, particularly in a first-person game. However, to the credit of THQ and Ukrainian developer GSC Game World, S.T.A.L.K.E.R. is an impressive accomplishment. This first-person survival game is at times amazing and engrossing and on par with such classics as Deus Ex and System Shock.

S.T.A.L.K.E.R. has finally arrived, and it delivers an impressively immersive and open-ended first-person experience.

This is another first-person game that features a silent and mysterious protagonist, much like Half-Life's Gordon Freeman. You play as the Marked One, a heavily armed scavenger suffering from amnesia and stuck inside the exclusion zone surrounding the nuclear power plant at Chernobyl, Ukraine. Yes, the same nuclear plant that exploded in 1986 and, in S.T.A.L.K.E.R.'s fiction, again in 1989, creating a radioactive hotspot brimming with mutants, heavily armed rival factions, and all sorts of weird, paranormal activity. Your task: Figure out who you are and what's going on at the core of the zone.

At its heart, S.T.A.L.K.E.R. is a first-person survival game that blends action with role-playing. This isn't a linear game, like Half-Life or Call of Duty, where you basically are restricted to a straight path and are taken for a tightly controlled and scripted ride. S.T.A.L.K.E.R.'s huge environments and open-ended gameplay make it more like a role-playing game, as you can go where you want and do what you want if you're willing to live with the consequences. However, you don't have to worry about traditional role-playing attributes such as strength or intelligence, or accumulating skills and abilities. Instead, all you have to worry about is your skill with a rifle and scavenging enough weapons, ammunition, and med kits from fallen enemies to keep going.

Slowly but steadily, S.T.A.L.K.E.R. introduces you to the bizarre world of the zone, a place where the fabric of reality is being ripped apart. Strange energy anomalies are everywhere, and wander into one at your own hazard. These anomalies produce rare and valuable artifacts that can be collected and traded, or even equipped, as they can confer special abilities. Perhaps the most useful ones enhance your endurance, letting you run for far longer than normal, which is a particularly valuable ability to have when traversing the huge area of the zone. And, of course, danger lurks everywhere in the form of enemies that are both human and not-quite human, as well as from animals.

To battle them, you'll have a large arsenal of weapons to eventually choose from, mainly in the form of assault rifles, shotguns, and pistols. S.T.A.L.K.E.R. features one of the best ballistics models ever seen in a game, and as a result, firefights feel authentic as you try and hit someone with what can be a wildly inaccurate rifle. The name of the game is using cover effectively and firing short, accurate bursts, particularly at the targets' heads. After a battle, you can loot the dead for weapons and ammunition, and one of the nice touches in the game is that you can't run around with an arsenal of 9 or 10 different weapons. Instead, the inventory system restricts what you can carry mainly by weight, and most weapons use a different type of ammo, which means that you've got to be judicious in selecting what you take with you. There's simply no way you can haul around three or four different weapons, their ammunition, and everything else that you need to survive in the zone. This includes health packs, bandages, radiation medication (vodka will also do in a pinch), and even food. You've got to eat regularly in S.T.A.L.K.E.R., and if you go too long without food, hunger warning signs appear.

The inventory system is like that in a role-playing game, and you'll spend a lot of time trying to figure out what to carry with you.

The game's artificial intelligence is impressive, both in and out of combat. In combat, enemies are cunning when given enough room to move around. Human enemies hunt you intelligently, using cover and the terrain to their advantage. Meanwhile, creatures such as packs of mutant dogs behave like you'd expect wild animals to. They attack when they feel they have the advantage but flee if given a painful lesson. It's this kind of behavior that makes the zone feel alive, with these different factions and animals all trying to go about their daily tasks. The AI does take a hit when placed in tight interiors, though, as the lack of maneuvering options makes it turn a bit predictable, but you'll likely appreciate this fact early in the game, as hiding inside a building and picking off the grunts as they come through the doorway is the only way that you'll survive some of the early battles.

There are all sorts of human characters in the game, from lone stalkers out on their own to various factions that you can ally with or battle. Then there are the mutants, from the strange animals that inhabit the zone to the more deadly kind of mutated humanoid, such as the little guy who can mess with your mind to the creepy crawling dudes who lunge at you from out of nowhere. Toss in S.T.A.L.K.E.R.'s version of zombies and poltergeists, and you've got a more-than-interesting array of potential friends and foes. There are some large-scale battles that will find you fighting alongside teammates, and afterward you'll watch as AI friendlies saunter up to the wounded writhing on the ground, say something nasty in Russian or Ukrainian, and then shoot them in the head.