S.T.A.L.K.E.R.: Clear Sky is a 2008 first-person shooter survival horror video game with role-playing elements. It was developed by GSC Game World and published by Deep Silver as a prequel to S.T.A.L.K.E.R.: Shadow of Chernobyl.
The player assumes the identity of Scar, a mercenary tasked with stopping a group of Stalkers from reaching the center of the Zone, a forbidden territory surrounding the Chernobyl Nuclear Power Plant. The game uses much of the same regions as Shadow of Chernobyl, while introducing several new areas such as the abandoned town of Limansk. S.T.A.L.K.E.R.: Clear Sky introduces features to the series, including the ability to customize weapon and armor, as well as participate in faction wars.
A third game, S.T.A.L.K.E.R.: Call of Pripyat was released in 2009 as a sequel to Shadow of Chernobyl.
Gameplay
This game combines elements of first-person shooters ("twitch-based" aiming, with a first-person perspective), survival horror (ammo-scavenging in a frightening atmosphere with powerful monsters), and role-playing video games (inventory management, quests, character interaction, armor types, and defense stats).
The most significant gameplay addition since Shadow of Chernobyl is the faction wars system. Different factions will struggle for territory, attacking to gain territory and then defending to keep it, while others then try to retake it. The player will be able to join and help factions in their battles. The stronger a faction becomes, the better equipment the traders can provide and their soldiers can use. The player character is a mercenary, and may do missions for any faction or remain completely neutral without disrupting the necessary progression of the game. Each of the main factions provide services, most importantly access to a trader and an engineer.
While Scar is always aligned with Clear Sky, and his ultimate goal is to defeat Strelok, he can fight against or ally with the four other factions in the Zone (Loners, Duty, Freedom, and Bandits). The Swamp-dwelling Renegades or the Military factions cannot be joined. Careful choice of faction alignment needs to be considered in some parts of the story, for it may be difficult to progress further if the Stalker who the player is interacting with is hostile, has needed information, or is essential to triggering the next stage.
Other gameplay advancements since the first game include a deepened weapon customization system with the ability to repair damaged gear and add modifications that improve weapons and suits. Anomalies are harder to notice and now contain the artifacts in the game, which require a detector to locate. Non-player characters are given the ability to use hand grenades, take cover dynamically, and use "blind-fire" techniques. Light machine guns have been introduced. There are guides in the zone who will provide fast-travel for a fee. Emissions, powerful waves that are sometimes visible or invisible (determinant by intensity), unleash lethal radiation, psi-emissions, and other unknown particles and energy directly from the Chernobyl Nuclear Power Plant, directly affecting the Noosphere in The Exclusion Zone, making it deadly to all lifeforms except specific mutants. Emissions also occur on an infrequent basis, requiring the player to take cover in a building or underground area pointed out by the PDA. If not adequately concealed, the player's nervous system shuts down, resulting in the player's death.
Plot
While guiding a group of scientists through the Zone, Scar faints during a high energy emission. Scar, the only one to survive, is then rescued by Clear Sky, a secret independent Zone faction dedicated to researching and learning about the Zone in their attempt to better understand it and its related phenomena. It is not known how Scar has survived the emission, but it is noted he has suffered damage to his central nervous system and seems to exhibit other, subtle physiological changes.
The nature of these changes becomes clear shortly. Word arrives that a platoon of Stalkers has come under attack by mutants, and Lebedev, leader of the Clear Sky faction, asks Scar to seek them out and help them. During the rescue attempt another emission occurs with little warning, giving Scar and the Stalkers no time to seek cover. Once again Scar is the sole survivor, recovering shortly after the emission dies down. Lebedev is amazed that Scar is still alive; the Clear Sky lead researcher, Beanpolev, believes that Scar has acquired some "unusual ability" that allows him to navigate and survive anomalies and parts of the Zone that would normally kill any ordinary man.