upon, this game is a treacherous, darkly beautiful terrain." Game Informer did not find the gameplay particularly innovative, but still complimented the basic FPS design, saying, "S.T.A.L.K.E.R. isn’t the revolution that we all hoped it would be. It is, however, a respectable and sometimes excellent first-person adventure" whereas GameSpot called it "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". Upon release, S.T.A.L.K.E.R. was criticized for having numerous bugs, especially when used with the then-recently released Windows Vista. IGN found the game "tended to stutter quite often, sometimes pausing for three or four seconds at regular intervals, which occurred on two different Windows XP computers at maximum visual quality," and some cases of game crashing glitches. Another criticized aspect was the story, which to some reviewers was "incoherent" and which PC Gamer stated "fails in the specific story of your character". Awards S.T.A.L.K.E.R. won the Special Achievement award for Best Atmosphere in GameSpot's Best and Worst 2007, stating that "S.T.A.L.K.E.R. captures the 'ghost town' nature of the zone, from the abandoned cities to the overgrown wilderness. Then, the game adds its own paranormal elements, which help make a spooky environment almost terrifying at times." Sales S.T.A.L.K.E.R. received a "Silver" sales award from the Entertainment and Leisure Software Publishers Association (ELSPA), indicating sales of at least 100,000 copies in the United Kingdom. As of September 2008, S.T.A.L.K.E.R. has sold 2 million copies worldwide. GSC Game World CEO Sergiy Grygorovych has said "We are very pleased that S.T.A.L.K.E.R. became so popular among players from all over the world. Financial success will allow us to develop S.T.A.L.K.E.R. in different directions as a brand." Legacy S.T.A.L.K.E.R.: Clear Sky S.T.A.L.K.E.R.: Clear Sky is a prequel set eight months before Shadow of Chernobyl. The game world consists of a mix of old, redesigned areas and completely new levels. The updated engine supports the Inverse Kinematics animation system, allowing more and better animations. New effects such as volumetric lighting were also included. In general, the developers sought to take the basics of everything in Shadow of Chernobyl and enhance them. Better AI, graphics and new game-play additions, such as faction wars, were some of the added features. S.T.A.L.K.E.R.: Call of Pripyat S.T.A.L.K.E.R.: Call of Pripyat is a sequel set after the events in Shadow