I just bought it last night, and so far I really like it. It seems to run better than the first one did while having better graphics. And the level design is awesome. My biggest complaint is Rochelle, I know everyone is saying the same thing but I think she is the weakest character.
Here is the L4D2 line up.
1 annoying ex convict who is on rare occasion funny - Nick
1 annoying uneducated redneck who is pretty much a stereotype - Ellis
1 annoying not attractive female - Rochelle
1 semi cool black guy - Coach
To be honest, they just should have put Lo Wang in there along with Duke Nuke'em, John Matrix from commando, and Summer Glau as the token female bad ass.