Originally Posted by GameSpot

Called Doom 3: Resurrection of Evil, the expansion is (unsurprisingly) set after the events of Doom 3, when the space marine uncovers an ancient and evil artifact in the depths of hell. Unluckily for him, the denizens of Hades want their malevolent knickknack back, leading to another round of fiery marine-on-demon action. Activision promises the game will hold "new locations, characters and weapons." The most notable new weapon to be featured will be the double-barreled shotgun, which made its first appearance in Doom 2. The new offering will require the full retail version of Doom 3 to play and has not yet been rated by the ESRB. However, it's a safe bet that the game will be rated "M" for Mature.