Yup. I don't get it. Here, link:
click.
Trailer.
Article.
Steam's official announcement.
Hm. I really don't know what to say, except that I'm extremely confused at Valve releasing this so soon (Nov 17th??), even though that probably means February 09, if they still work in Valve time.
New special infected types(the old ones are still here), new zombie types, new explosive ammunition, new weapons, revamped AI Director, takes place in the New Orleans area.
Oh, and new characters.
Oh, and here: