Valve Software was a pioneer in the field of digital distribution, setting up its Steam online store as a way to deliver full-scale games like Half-Life 2 to consumers directly through the Internet. Now the company is using its flagship franchise to explore another emerging field in the gaming market, episodic content.

　　Copies of Half-Life 2: Episode One downloaded through Steam were unlocked at 10 a.m. today as the game also went up on store shelves around the world. The stand-alone game picks up where Half-Life 2's cliffhanger ending left off, and moves the story away from the City 17 setting of the original game.

　　In anticipation of the Episode One release, Valve took the opportunity yesterday to update its Steam digital distribution service. The newest update to the Steam client software makes a number of changes to the service's set of features. Among the more notable tweaks: the Friends feature has emerged from its Beta testing period, the back-up utility has been made quicker and more reliable, and content has been added to the Source engine that will allow it to support unspecified newer features.

　　Half-Life 2: Episode One is rated M for Mature and retails for $19.95 both online and in stores. For more on the original Half-Life 2, check out GameSpot's full review. For more on Episode One, read through GameSpot's latest preview of the game, and check back soon for a full review.