IGN: Dean slipped over the edge in last week's episode when he beat the snot of Castiel and killed the Styne kid, and the actions apparently started a downhill slide to the dark side. It was like he flipped a switch. The personality change was jarring and in some ways, the new Dean fell too far too fast. But that was kind of the point. He's given up. He's haunted by what he's done, he's hopeless, and he doesn't care. It was brutal.