I say Left Four Dead 2.
What a lot of people have already have said Uncharted was released a year before and was heavily bundled.
There are some things against L4d as well. Like some people have said it is going up against Modern Warfare 2 and Halo 3: ODST.
I really do not see it releasing a year after it's predecessor to be that bad. Look at games like CoD and Madden. They have yearly releases, yet do great numbers yearly.