Well not totally but a little perhaps.
This new Campaign is supposedly the most important yet, featuring both sets of survivors and certainly sounds like the most story-based section of the game I've heard of yet. IGN have the full scoop here
What will really surprise me is if it costs money for the PC crowd which, for the first time ever, I predict it will. There's very little chance it will be free for the xbox peeps and surely the question that has been asked by them is "Why just us?"
And why just them indeed, when PC users have been getting lots of lovely free content for Valve products for so long, why should they have to pay and not us? Well of course we're quite happy with the way Valve have treated us with the TF2 updates, which even now are still coming thick and fast after 2 years! There have been plenty of comparisons of this to the L4D series updates which have been far less speedy in arriving and even less satisfactory.
Perhaps then this will mark a change for the series? Now as far as we've heard this is Valve's fastest selling title yet - but is that on PC? If this add-on is announced as free then perhaps it could boost PC sales (if they do indeed need boosting and I have no evidence to support the idea that they do!)
Even so, this is the most interesting thing I've heard about L4D2 since that awesome trailer from just before it's launch. Let's hope this doesn't dissapoint!