Nope. L4D (tew) should be an add-on at best. "Why?" you may ask... if you didn't then don't read on...
Anyone playing Team Fortress 3?
There's your answer.
TF2 is still going strong and constantly updated, tweaked, and has had multiple content additions of which I didn't pay a dime after initial purchase. Still no TF3, and it's been out how long... so that leads me to wonder about this little social experiment. They're wondering if people will pay full price for a ver 2.0 based off a mod, from a game. I'm guessing yes, in droves.
Speaking of TF2, it looks like the Heavy and the Scout models made the L4D2 cut with a few cosmetic tweaks.
Screw L4D2, I wanna play L4DTF2+1, which will be the final evolution where they fully involve the TF2 cast and weapons, with L4D environment and objectives.