I herd talk about them making a third. Due to the fact that when Left 4 Dead 2 came out a little shy of a year after L4D, people were kinda upset cause they were still rummaging through and adding content to the first. They'll probably sit on it a while. No matter the time limit and since Valve has used the same engine since the dawn of time, the graphics will be only slightly enhanced from the other two. Rely on new enemies and a different set of survivors.