Left 4 Dead 2 campaign set in the fictional Fort Harris County. Four survivors must make their way through the zombie infested city to escape the zombie apocalypse. This campaign spans three different times of day and features different environments in which to perfect your zombie slaying prowess!
This campaign is so god damn good, I'm surprised that valve didn't hire the dev team! Hell, it was such a fun campaign that I really thought this was a valve map that never got finished or released until now!
In fact, I enjoyed this map more then any of the default campaigns, and it just plays so well!
And let's not forget the amazing Portal 2 easter egg that was put into the last level of the campaign!