Half-Life 2: Episode 1 (previously known as Half-Life 2: Aftermath), the official expansion to Half-Life 2 has gone gold and is expected to hit the stores by the 1st of June. The game picks up from where Half-Life 2 ended with Gordan Freeman (you're game persona) and Alyx fleeing City 17 after messing it up big time. Since Freeman's destroyed the Citadel, the creatures that were once kept at bay have now entered the city and have started wreaking havoc on its inhabitants.
Episode 1 will be the first in a trilogy of episodes that'll conclude by December 2007 and will feature new levels, newer weapons, a new single player story and two MP games.
The game will be around four to six hours long (its “episodic” content so you can't expect a full-blown game).