I have been craving a Meaty Coop game for a long while now, and leave it to Valve to nail it!! 

I love how valve made a bunch of design decisions throught the game to make all of players work together. Like getting slowed down when you are hit, needing every team member the helpful in game character chat (like when they shout out weapon caches, or when thay are realoading-beleve it or not that helps!), and curbing the "lone wolf" syndrome that plagues most online shooters.

They were able to make a creative versus mode that is not only creative & fun, but unique as well. As an infected I have had to make up stratagies on the fly that I never thought I would in a game. Each of the infected has a unique playing style with the hulk-like tank taking the cake in terms of being a riot to play.

Only downside is hoping that Valve can get DLC on the 360 quickly.