Originally destined to be a RTCW add on, 'Enemy Territory' has since become such a comprehensive project that this status is set to change as it becomes a standalone game! It shall soon be available for modders to unleash their skills onto!, in the mean time Computer and Video Games has an interview with id Software's Todd Hollenshead, and Activision's Jonathan Moses, where they discuss this newly upcoming game:
What were your reasons for making Enemy Territory stand-alone?
Hollenshead: Well, I think the big thing was that we didn't want to have ownership of Return To Castle Wolfenstein to be a factor in the purchase of it. If you really liked the things in Enemy Territory, or you really were a hardcore multiplayer fan and you wanted to do the cool stuff in the multiplayer, you didn't have to buy Return To Castle Wolfenstein first. And then from a content standpoint, I think that a lot of the stuff we wanted to do really lent itself to shipping an executable with the game.
So it doesn't include the original game, then?
Hollenshead: No, it doesn't include Return To Castle Wolfenstein.