The game is played from a third-person perspective in an open world environment, allowing the player to interact with the game world at their leisure. The player can travel the virtual world, a fictionalized version of the Western United States and Mexico, primarily by horseback and on foot. Gunfights emphasize a gunslinger gameplay mechanic called "Dead Eye" that allows players to mark multiple shooting targets on enemies in slow motion. The game makes use of a morality system, by which the player's actions in the game affect their character's levels of honor and fame and Redemption was acclaimed by many reviewers, with praise directed at the game's visuals, dynamically-generated music, voice acting, gameplay, and story. The game has shipped over 15 million copies and won year-end accolades, including Game of the Year awards from several gaming publications. It is widely considered one of the greatest video games of all time. After the game's release, several downloadable content additions were released; Red Dead Redemption: Undead Nightmare, later released as a standalone game, added a new single-player experience in which Marston searches for a cure for an infectious zombie plague that has swept across the Old West. A Game of the Year Edition containing all additional content was released in October 2011. A prequel, Red Dead Redemption 2, was announced in October 2016, and is scheduled to be released in October 2018.