Looking at this poster, you might think that it's genuine. But looking at that 99,999,999 countdown, you might think otherwise.
These Episode 3 teases are not uncommon. After all, everyone knows gamers' soft spot is for Valve's hopefully incoming Half-Life title. They're going to have to dispel rumors of an inability to count to three somehow, right?
Update: Looks like Kotaku reader crazydog115 discovered this troll/joke poster is even more trollish than meets the eye. It appears to be a photoshop of a Diablo III poster. We originally posted this to share what we thought was a Best Buy joke. Turns out that we didn't realize the whole is a photoshop. This picture is of something that doesn't exist. Like any future Half-Life game.