My only experience of Left 4 Dead 2 is a handful of sessions in my youth where a friend handed me a controller (me, a person whose shooter experience extended to Ratchet and Clank at the time), told me nothing, and let the chaos unfold. I did not do a good job. But it left a lasting impression! Though perhaps that impression would have changed had I seen its cinematic trailer as soon as Valve had wanted to release it.