How long does it take to make 4 short chapters and make small changes to the the character models anyhow. Hell, Valve couldn't even be bothered to make more than one survival exclusive map, instead they just allow you to use sections of the campaign map. I'll be surprised if we get more than 2 more special infected, and the 2 we get will most likely be the unfinished ones from the last game (A dog will be one of them).
Left 4 Dead isn't about atmosphere and suspense, its about fighting off hordes of zombies in a more action style shooter. Those wanting a zombie survival will be disappointed, but that doesn't mean this wont be worth checking out.
I believe i saw somewhere they going to add "the charger" or shall i call it a Fleshpounder?