Actually I didn't know what Left 4 Dead 2 was in general. Looked like some zombie game, but it was in a good deal, so I get it.
In the end, I had a looot of fun with it - it is pretty cool :-) It's a bit like the Serious Sam Games, where you do some Missions blowing away enemies and do the same in Coop. I like Coop!
So in Left for Dead 2 you are on guy in a group of 4 (either played by players or by AI) and have to survive a zombie apocalypse with different guns. This is one of better ones, I tell you. It is linear, yes .. and the campain is more some sofrt of different "stories" .. so it looks all a bit loosy.
But I liked it - it's a good quality game and if you see it in a deal and want to kill some zombies in different game modes and with fast action - grab it without a doubt. It will spend you some pretty good time :-)