L4D2 is a vast improvement in L4D in almost every respect. It actually has a plot for starters. Each chapter flows into the next as the four main characters try to escape hordes of the infected. That's right! They're not actually zombies folks! They're just humans infected by a virus that makes them exhibit zombie like personality traits, a plot line also been used a million times. But the plot is really not what matters here, it's not supposed to be important, as much as the plot as I got from the game without trying to find it was "Here are some zombies, here is a gun, have fun." What we're really here for is the gameplay.
In addition to your weapons you can hold presents such as Molotov's or Pipe Bomb's, the latter of which is incredibly useful and incredibly awesome to behold. If you don't enjoy hundreds of zombies piling together then have their exploded body parts ragdoll through the air then something clearly went wrong when God was handing out the human brains and bird brains.
Along with your dopey common infected are the more dangerous and lethal special infected who can ravage through a player's health in a matter of seconds as well as separate them from the group. These zombies must be brought down together and the players must constantly stay together to rescue each other from these zombies unless they want to lie down seductively on a dinner plate instead. The strongest of these are the Witch and the Tank, The Witch being able down a player in a single hit and The Tank having ♥♥♥♥♥♥♥♥ly insane amounts of health. All four players must stay together and work together to progress through the levels and do what is required of them depending on which chapter they are playing. The inclusion of these special infected zombies makes the game much more interesting and challenging than other zombies as well as bucketloads more fun.
While playing through the same five campaigns may not seem like a good length for a game, this is made up by the other modes L4D2 brings along. There's the usual survival mode that almost every shooter has nowadays. Scavenger mode where you play the worst ♥♥♥♥ing part of the game over and over. And Versus mode where you get to play as one of special infected zombies in a team of four and try to stop the humans from reaching the safe house. This is one of the few games where I actually enjoyed the multiplayer, maybe it's because the game is focussed around it but that's beside the point. Versus mode kept me entertained for hours on end and even now I would go back and play it.
The real reason that people can replay L4D2 over and over even though it's the same level is because of a bit of smart programming called the "AI Director." The AI Director has the ability to change the placement of walls, weapons, power ups and items in each level as well as being able to spawn hordes of zombies and special infected. This is done to an extent on one level on the fourth play through I was still discovering new paths through the level. No game has anything else like this and it is a unique bit of programming on Valve's behalf.
BUT, remember that sentence about body parts flying through the air? Well that is in the game, but not in the Australian version. The Australian version of L4D2 has been cut down and censored to fit under the MA15+ label as we have no R18+ classification. Even Valve themselves were startled and confused by the refusal of the classification and I can understand why completely, the original game is not that bloody or violent that it would need to be banned. So say goodbye to corpses, body piles, gore, dismemberment and decapitation, apparently if we see that we will all turn cannibal and eat each other.
Left 4 Dead 2 is a standout game that deserves the praise it gets. The gameplay is highly entertaining with good replay value due to the AI Director as well as beautifully atmospheric. The online multiplayer is actually quite good which coming from me is a massive ♥♥♥♥ing compliment so go out, buy this game, and witness it's mastery.