Anyway, mine has got to be Semper Fi Or Die - The "defend area against aliens" part was easily the most enjoyable part of the game, a garrison of weapons to choose from, different enemies (Would've been better with pingers as well), and a gunship fight at the end.
For the love of defending an area with friends, no-one I know would not want DLC to do just that.
I mean, the level design for it was genius - sort of like a base.
I'd play that mission just to get to that part. Now if only it had lasted that little bit longer.