Technically, I'm aware that the employees of Valve have regular jobs, doing regular things on irregularly mobile desks. Even so, when picturing Clint Hocking's year and half stint with the company, I can't help but imagine him strapped into a central development node, where tendrilled mind probes extract creative ideas to be fed into the Almighty Feedback Formula. I'm not saying that's definitely what happened, but if it is, it's perhaps understandable why he'd leave. Which he has.
News of Hocking's departure comes via his LinkedIn account and personal blog, where his biography states: "From 2012 until the end of 2013, Clint worked as a designer and level designer at Valve in Seattle."
Hocking is probably best known for his work at Ubisoft, where he was creative director for Splinter Cell: Chaos Theory - a game that, to this day, remains the highpoint of that series. He was also the creative director for Far Cry 2, which is either the best of the worst Far Cry game, depending on your fondness for emergent situations, jamming weapons and malaria.
In typical Valve style, we don't officially know what Hocking was working on. But based on leaked information taken from their internal database, he was suspected to be part of the team developing the yet to be announced Left 4 Dead 3. As yet, there's no information about his next project, but hopefully it'll evoke the same manic clash of systems that defined FC2's best moments.