A concise list of what people are actually angry about – Steam Users’ Forums.
The above thread shows what a shock anouncement it was to people who heard the E3 announcement of L4D2, people feel ripped off(including myself) dissapointed and disjointed with the “once” can’t do anything wrong team at Valve who have subsequently pissed off a very large user base of L4D.
Hopefully they make it right because reviews coming in aren’t all that good.. looks like a mod, feels like a mod but a Full Price Game?

Edit: Oh and if the above link doesn’t work for it means they have removed and censored the outrage. Just incase they do like the other threads that are already removed.