This thing has been a rumor until it was officially announced by VALVe.
I, like most people think that this is some kind of joke. Left 4 Dead isn’t even a year old yet, and they’re already working on a sequel.
The characters have changed, and so have the boss enemies. There’s a slightly changed HUD, new weapons, new maps, and AI Director 2.0.
If you want my opinion, I’d say they’re trying to redo L4D the way I thought it would be in the past.