Know what's awesome? Left 4 Dead 2. You bet it is.

You've played Left 4 Dead, right? You have? Good.

Wait, you haven't? Get out.

Wait, come back. You can stay.

I SAID YOU COULD COME BACK

PLEASE COME BACK

Long story short:
-It's harder (but in a good way)
-Lots of new stuff to play with, for both Survivors and Infected
-Almost no corner camping
-Versus is now a competition to see who makes it the farthest, not who makes it with the most health. Expect to die a lot in that mode
-Awesome setting
-New cast of interesting Survivors
-It's better
-Go buy it

I'd go into more detail, but time spent telling you about it is time I'm not playing it.