i get it in pretty much every game where the stories isn't "SPACE NAZI FROM HELL ARE HERE TO TAKE OVER YOUR LAND, FIGHT THEM". it seems especially strong with games that have narrative that connects on different levels (after playing aquaria or mass effect1/2 i couldn't really press myself to play anything for a good few weeks afterwards). the x-files did the same to me when i finished watching them (actually before i finished, the last two seasons without mulder was like removing the soul from the series).
the funny thing is, it's never a good feeling. despite the games being excellent and awesome, it just seems like a depressive after burner.