But, the game world is not one big world, but is a lot of smaller maps broken up by loading screens. The Zone is made up of a 30 km square area, that has wilderness, human camps, and a few heavily-guarded military bases. Unlike RPGs such as Knights of the Old Republic, the number of different conversations the player can have with NPCs in the game is quite small and does not change the way that the game will end for the player a lot. But, the game does not let the player have a lot of choice when it comes to talking to characters in the game.
The role-playing part is mainly about normal RPG elements, such as storyline and the way other people in the game act with the player. The type of game is a mix of a RPG and a FPS, though the player does not get attributes like Strength of Constitution, or get more powerful, which is different from a normal computer RPG. In the game, the player is known as "The Marked One" who is a Stalker, a person who lives in the Zone and makes a living collecting "Artifacts" and selling them. So, the game will have some idea of fight or flight to it. The animals anger will vary with how hungry and tired they are, as well as other things. IGN said that the game, while similar to Far Cry, will have more wildlife, and that the way animals act in the game is as important to them as the humans. GSC Game World talked about the game's AI in January 2005.
Some phrases used in the game ("The Zone", "Stalker") as well as the idea of the game, are borrowed from the popular science fiction book Roadside Picnic by Boris and Arkady Strugatsky and the 1979 film Stalker, based on the book. The game includes features of role-playing and economic games. The game has a storyline that lets the player have a lot of freedom, and features gameplay features such as trading and two-way communication with NPCs. It features an alternate reality theme, where the second nuclear disaster happens at the Chernobyl Nuclear Power Plant in the near future and makes strange changes happen to the area around it, which create a lot of mutated animals, plants, and change the laws of Physics. The game uses a software feature called the "X-Ray engine". S.T.A.L.K.E.R.: Shadow of Chernobyl, previously known as S.T.A.L.K.E.R.: Oblivion Lost, is a post-apocalyptic first-person shooter video game by Ukrainian developer GSC Game World.