From the developer:
Wolfenstein Enemy Territory is a free, stand alone, downloadable multiplayer game in which players wage war as Axis or Allies in team-based combat.

Do battle in traditional single scenarios, or wage war through a series of linked scenarios in a totally new campaign mode. During combat players gain experience and skill, and through battlefield promotions are awarded additional abilities that remain persistent across an entire campaign.

Additionally, new character classes like the Covert Ops as well as enhyanced Engineer allow teams to perform reconnaissance, steal enemy uniforms, and construct battlefield structures and military installations in the midst of combat to gain tactical advantages for their team.

All new game modes, maps and communication abilities require players and teams to develop advanced strategies and tactics in the struggle for front line domination.