Half-Life 3 is an open world shooter set for release sometime after 2013. The news comes by way of an annonymous source close to Valve. 

Speaking with Journaldugamer as translated by OXM, the mysterious source claimed that Half-Life 3 was set to be just another linear shooter, but saw a "total revision" after a "very chaotic" development cycle resulted in many delays and re-writes. As a straightforward shooter, Half-Life 3 "failed," so the decision was made to set it in an expansive open city. That open world territory will naturally bring with it "quests and NPCs" in the vein of Assassins Creed III and its side missions. 

Several other RPG elements are said to be entering the mix, although what that specifically means has not been elaborated upon. 

The game is said to be well along in development, although with such an ambitious and highly-anticipated title as this it's only natural that the team face a slightly protracted dev cycle. Don't expect to see Half-Life 3 until 2014 at the earliest.

Of course without any official confirmation from Valve, this is all just rumor. But an open world Half-Life game does sound pretty tantalizing, doesn't it?