In the interests of full disclosure: I never played the original Left 4 Dead - are you kidding me? It came out four days after Wrath of the Lich King! So if you're looking for an opinion on that whole brouhaha about whether or not it's different enough from the first game to be a full-fledged sequel instead of an expansion pack, you won't find that here. What you will find is this: Judged on its own, standalone merits, Left 4 Dead 2 is an awesome, awesome experience.
The premise is the same as the first game: Four Survivors have survived the apocalypse thanks to being immune to a virulent disease that turns all who are Infected into ravenous, murderous monsters - zombies, essentially. The Survivors must work together in order to survive and reach safety, and on the way they'll blast and chop their way through the Infected to get there.
The lucky (or unlucky?) quartet this time around is Rochelle the ambitious young journalist, Nick the drifting con-man, Ellis the energetic redneck mechanic, and Coach the, uh, coach. While fans of the first game may miss the original four Survivors, the newbies are all endearing in their own right, and their dialogue is well-written - Ellis may well be one of the funniest characters I've seen in a game in entirely too long. Certain phrases will get repeated enough to become rote and commonplace, but I'm still hearing new things after 30+ hours of play, so make of that what you will.
The Survivors will be fighting for their lives in five new campaigns set all across the American South from a shopping mall in Savannah to the grand finale in New Orleans, and while there's a bit of storyline connecting the scenarios it's hardly on the level that some were expecting. Still, the game isn't any weaker for it, and the individual stories gleaned from the writing on the walls in the safe rooms speak loudly enough on their own.
In a way, perhaps it's almost refreshing that Valve hasn't subjected us to lengthy overwrought cutscenes, because it would get in the way of the game's zombie-slaughtering good time. All of the guns in the game - new and old alike - feel powerful and entertaining in their own right, but the real fun is in L4D2's melee weapons. Maybe it'd be more prudent to hang back and blast the Infected with an M16, but there's something viscerally enjoyable about wading into the fray and chopping heads with a fire axe. And I do mean visceral - Valve has upped the gore tremendously in this installment, and chopping off limbs will reveal the splintered bone beneath, a shotgun blast to the chest will expose the rib cage, so on and so forth. No wonder it got banned in Australia.