Okay I lied. It's nigh impossible not to click on a thread you've posted previously in.
I enjoyed Rock, Paper, Shotgun's preview of it.
The more previews I read up of the game, the more it seems like they've expanded on the game. Could they have patched this stuff into the game? Possibly. Maybe even probably. But it seems to me that these patches would have altered an awful lot of the L4D game. So much so that it would literally seem like a different game. Especially things such as the dynamic level layout (which I doubt could be patched into the game).
Some of the easier additions, though, were likely decided to be added to L4D2 to create more reason to purchase L4D2 (lets be honest here, Valve is a company in this to make money). Ironically, I think that releasing these smaller additions would further diminsh L4D2 as a standalone game, and the ire of upset gamers would not be quelled.
I know it's easy to say reviews and previews are bought out and meaningless, but I haven't seen any (admittedly I haven't seen many period) that weren't explicit in stating to readers that they felt this was more than just a little expansion.