How does this answer the calls of the L4D2 boycott crowd?. If anything it makes, some of, their points more valid.
Surely adding more content to L4D, so close to the sequel's intended release, shows how pointless L4D2 is when Valve could still be adding to the original. Doesn't this reinforce the claim that L4D2 would split the community, as people will have a new incentive to play the first game?
If you believe this a response to the boycott group, and its hard to see it otherwise, then it really reinforces the question as to why there weren't more campaigns added to the original via DLC before now. If a new campaign has been produced in a relatively short period of time, while they're working on L4D2 as well, then surely they could have produced another three or four by now if they hadn't been intent on making the sequel instead.
While I appreciate this, and will definitely download the content, it makes me want L4D2 less as it makes it seem more likely that there could well be more stuff on the way. Why bother with the sequel when there's still life in the original?