Although zombies have been a part of pop culture for decades at this point, it seems like they've become thoroughly embedded in recent years. In the wake of 28 Days Later and the 2004 Dawn of the Dead remake, it's been impossible to avoid zombies showing up in books, movies, and of course, games. Valve's Left 4 Dead comes across as an homage to all of this, and should rightly be essential gameplay for any zombie fan.

Outbreak

On a superficial level, the premise of the game is extremely simple: an infection has spread across the U.S., turning most of the population into fast-running, 28 Days-like zombies. In most circumstances, players control one of four immune survivors - Bill, Francis, Louis or Zoey – as they attempt to escape from one saferoom to another, and eventually find some sort of rescue.

This means killing plenty of zombies of course, and players gun them down using a collection of rifles and shotguns, with one or two pistols as backup. More effective tools include Molotov cocktails and pipebombs, the former of which incinerate zombie hordes, while the latter actually attract zombies before consuming them in a bloody explosion.

One highlight of L4D is its maps, which seem to borrow almost subconsciously from every major zombie movie you can think of. These are divided into four campaigns: “No Mercy,” for example, has players run through (and under) city streets to reach the roof of Mercy Hospital, while “Blood Harvest” has players track through moonlit forest and farmland. Each contains set pieces that appear immensely familiar, such as the infested hospital, and more than one abandoned house under siege, a la Night of the Living Dead.

Because killing the same basic type of zombie in different clothes might become boring after a while, Valve has also included five special types, bound to raise panic whenever they appear. Hunters are able to pounce on humans and tear them to bits; Smokers rope players in with their tongues, and the boomers will either vomit or explode all over survivors, luring in the rest of the horde. Witches – which take the form of crying young girls - are one of the most insidious types, since they're not only hard to kill but seemingly easy to avoid until you spook them. Tanks are nigh-on invincible, and can sometimes wipe out several players single-handedly.

And cut

Perhaps your greatest enemy though is the AI Director, which also happens to be the greatest feature of L4D. The Director keeps the pacing of the game even, neither too easy nor too intense; it does this by judging the location, state and competency of players, and then hurling varying numbers of zombies at them from quasi-random directions. The system additionally metes out weapons, ammo and health supplies at random locations, meaning that you can never assume they'll be in the same place twice.

You can never assume that zombies will be in the same place twice either, which is where the genius of the Director lies. Players are continually caught unaware by zombies climbing up walls, breaking through doors or rushing out of the wilderness. Aside from producing the suspense one would hope for from a zombie movie, it means that even though the maps are relatively linear, no playthrough is ever exactly alike. This proves to be crucial, since players will likely go through a map many times, often during the same session.

Escape routes

I say session because while you can play the game as a single-player title, it defeats the point. Actually, it does hold up surprisingly well in single-player, if only because the environments are so atmospheric, and you're guaranteed a continuous supply of random carnage.

The heart of the game is in multiplayer, which in turn is about co-operation. In the Campaign mode, two to four players try to survive a scenario, with the AI filling in for any missing humans. At least one character has to make it to rescue, which isn't as easy as it sounds; not only are players under constant ambush, but the end of each campaign tends to involve a massive siege, in which it's virtually guaranteed that one or more players will die.

The remedy to this is sticking very, very close to your teammates, and making sure everyone's on the same page - failing to do this means being caught without a helping hand. On top of this, some hardwired mechanics reward people for being nearby. Players can share pills and first aid kits with each other, and before you die, you're normally knocked to the ground first and limited to using pistols. Much as in Gears of War a teammate can then pick you up, which increases everyone's odds of success.

What will probably sell some people on L4D, though, are the stories that naturally arise. It's common to find yourself standing guard over a downed friend, fending off enemies; then there are moments like slamming a door shut just in time, or making a last-ditch sprint to a helicopter as zombies overwhelm the walkways. Valve has managed to recreate more than just the setting and characters of a zombie movie, they've also managed to capture those little plot points that make one exciting.

Second skin

More stories are possible in the Versus mode, which follows the same general structure as Campaign but allows another four players to control the special zombies, with the exception of the witch. Unlike the humans, the zombies get infinite respawns, and can choose where to spawn so long as it's not in sight of the human team. This brings a new level of tension to the game – the AI is dangerous enough on its own, let alone with the help of people scheming to appear at just the wrong moment. Some really diabolical traps and massacres become possible when zombies cooperate.

The tragedy of Versus is that at present, only two campaigns support it: the aforementioned No Mercy and Blood Harvest. Death Toll and Dead Air are excluded for some reason, which limits the replayability of what should be L4D's most popular mode. Replay value may be an issue for some people overall, given that the maps inevitably lose their novelty; that being said, there are more maps by default in L4D than there are in either Counter-Strike or Day of Defeat.

More controversial for the PC version may be the matchmaking system for the game, which abandons the familiar server-based join method for Xbox Live-like matchmaking. Dedicated servers exist, technically, but you can't browse through them in a normal fashion. The easiest way to get into a match thus becomes searching for lobbies, creating your own, or joining a friend's game. I find myself using the last method a great deal of the time, since any team-based game is infinitely more fun with people you know.

A minor criticism is that under player control, tank zombies are almost ludicrously overpowered. Enough of a bullet sponge without human intervention, they subsequently gain the ability to wipe out a whole team of survivors, at least in a closed space. Valve may be aware of the issue, but at the time of writing this, tanks could still stand to be nerfed a bit.

Day of the dead

Unless you're genuinely lacking anyone to play it with though, Left 4 Dead is easily one of this year's must-have games. There's a kind of fun it produces which is rarely found in titles of any genre, let alone something which makes an effort to cater to zombie fans – it's the fun that can only come out of good co-op play with friends, something publishers are finally starting to realize. The real test for the game will be longevity, since online play could peter out in just a few months without extra campaigns. I suspect they're coming however, because response to the game has been extremely warm so far.