Regarding The Passing DLC, here's what the company had to say:
Revealed back in December 2009, The Passing will see survivors from the first Left 4 Dead meeting up with the group from L4D2. About a month after The Passing is released for Left 4 Dead 2, the original L4D will get new content detailing the journey taken by Bill, Zoey, Louis, and Francis to meet up with the cast of L4D2.
Was that a typo? Game Modes? Didn't we mean Game MODE? Did we mean to include that 'S'?!?!?"
- A Wicked Witch Bride!
- A Gargantuan M60!
- A Slashing Golf Club!
- And Introducing The Fallen Survivor!
- Meet 3 Left 4 Dead 1 Survivors!
- New Game Modes!
YES WE DID!