Left 4 Dead 2 DLC

Minding my own buisness on youtube, suddenly I find this trailer. I barely played Left 4 Dead 2 at a friend played the first single player, so i got to say i haven't got much experience with the series, and if you ask me killing zombies all day long DOES get boring, however this DLC may have a storyline, which is all that i want more from the series.
Please enjoy and 'till next time, e-dwellers.