i dont think... its just l4d1 addon.
I have to say if you paid the 28 bucks for the four pack a few weeks ago, yeah it was worth it. I was lucky enough to take advantage of that with some bros and i gotta say i got my moneys worth. it makes the first game unplayable.
L4D2 is my new favorite game for the 360. It's stunning. Perfect mix of rpg-style missions, great back story, awesome new game modes, and the same intensely satisfying fps experience. I loved the first one, but the second one is by far more intense.
I still can't complete a campaign on expert though, whew.
Need help? PM me and I'll find you the answer.