There are also several underground maps such as the X10-X18 series of experimental laboratories. It features large open maps, populated by mutants, friendly and enemy NPC characters. The game is a non-linear, open world shooter, which falls heavily on the FPS side of the FPS RPG genre. A prequel, S.T.A.L.K.E.R: Clear Sky, was announced by GSC Gameworld in 2007 and released to mixed reviews. S.T.A.L.K.E.R.: Shadow of Chernobyl is a first person shooter developed by Ukrainian developer GSC Gameworld, and published by THQ in 2007.
