the Death Toll campaign from the original Left 4 Dead on the PC-playing Left 4 Dead 2 crowd today, albeit with some minor tweaks which Valve is being mum about. They want us all to go in with "fresh eyes" they say, so we'll see how that goes. Any feedback you have, you can drop it in the Steam forums. (Or you could leave a comment in this very post!)
Also, Valve's got an update on the launch window of the entire Cold Stream DLC release, of which Death Toll is a part of: It's coming around Halloween. Previously the goal was late summer, but with all of the testing and rigmarole that goes into tuning a game, Valve's gotten a little behind schedule. It's tough to complain, considering how very, very free all this stuff is.