The expansion pack does not add new campaign content in the conventional sense, rather adding a "Virtual Voyager" mode to the game, allowing the player to explore ten more decks of the ship. Within these ten levels, the player can interact with a variety of characters, collect secret items and operate various ship functions such as using replicators, reading characters' personal logs and accessing the ship's computer files. Two new combat campaigns are added, integrated as holodeck programs; the first revolves around Tom Paris' black-and-white Captain Proton hobby, while the second is based around an infiltration mission into a Klingon base. In addition, five new multiplayer modes were introduced.
Source: Wikipedia, "Star Trek Voyager: Elite Force," available under the CC-BY-SA License.