In 2003, the retail release of Wolfenstein: Enemy Territory was cancelled, and its multiplayer mode was given away for free. As id and Activision said at the time, "Despite a strong effort from talented developers, the single player portion of the game did not progress as anticipated." Enemy Territory ended up becoming a formative multiplayer shooter, and its influence on the genre is still felt today. But players have always wondered: what would that singleplayer campaign have been like?
Modder William Faure has one answer, with a mod that takes Enemy Territory's maps and connects them together to form a story-driven campaign. There's a trailer for it above, featuring a rad metal version of Für Elise and a whole lot of Nazi-shooting action. A co-op version of the mod will follow on November 30, and is currently in testing.
To play it you'll need to have Return to Castle Wolfenstein installed as well as one of its overhaul mods (iortcw, RealRTCW, RTCW4A, RTCW-Touch, vitaRTCW, or RTCWQuest). The Enemy Territory singleplayer mod is available on ModDB and the Steam Workshop.
If you're interested in the saga of how this foundational FPS series was passed from developer to developer over the years, here's the history of Wolfenstein.