Left 4 DeadPlatform:PC, Xbox 360
Publisher: Valve (digital), Electronic Arts (retail)
UK Price (as reviewed):£19.97
US Price (as reviewed):$44.99

Zombies. Co-op. Steam. For those of us who like our action geeky, gory and varied, it’s like a dream come true.

Ever since the pre-order demo dropped onto Steam two weeks ago our lunch times, our evenings and our weekends (and in Joe's case his girlfriend's entire life) have been filled with zombie blasting, flash light flailing mayhem, and despite only featuring one and a half levels from the full game, Left 4 Dead has kept us, and many of those on our Steam friends lists, coming back for more time and time again.

It’s easy to see why Left 4 Dead is already so popular because in many ways it’s almost the holy grail of PC gaming. It’s made by one of the best developers around, who are pushing it on one of the best distribution platforms around, it’s playable in singleplayer, multiplayer and co-op and it’s very replayable.

Hell, it’s even built on the popular and constantly improved Source engine. While that does mean that the game can look a bit dated in places, it also means that it's perfectly playable on nearly all computers from the last five years and that the modding community can quickly latch on - even in the short time since the demo we're already seeing other Valve content converted in zombie massacring battlegrounds.

It’s the replayablity which is the most interesting factor to us though. The game uses a dedicated AI system to track the progress and ability of players, moving items and enemies around to provide a unique experience every time. More than that, the AI Director has a basic understanding of pacing so that the game can have lulls and peaks in all the right places.

That’s one of the most complicated things about Left 4 Dead though and while it is something all players will need to appreciate, it isn’t something many will need to understand.

So here’s what you need to know. The world of Left 4 Dead is set in that most easily explained of fictitious scenarios, the Zombie Apocalypse. The fast-zombie apocalypse to be precise (slow shufflers just wouldn’t be as entertaining would they?), with five more unique boss zombies tossed into the mix such as The Boomer, horribly obese and intent on vomiting on you to attract the zombie horde, or The Hunter, who can pounce long distances and pin you to the ground.

One thing that all the zombies have in common though is that they are between you and the next safe haven and that they’ll drop dead for a second time after a liberal application of lead. Thus the twenty-level stage is set as you and three other survivors, controlled by either AI or other players depending on what you want, begin an epic journey to rescue.

The game is divided into four campaigns split between five levels connected via safe havens, and while all are based upon the same premise of a trek through zombie infested territory each has a unique feel thanks to the surprisingly varied environments. One campaign begins in a green house on the ruins of a small town before climaxing on the tarmac of an airport runway, while another sees the survivors journey to the top of a sky scraper to reach rescue.

The zombies will come in mountains, hordes, swarms and waves all at once and you’ll have to keep a close eye on your team mates and ammo counts as you meet the gibbering menace and try simply to survive another day. Are you up to it? Of course you are, but are your allies? You’d better hope so because it’s going to take coordination and teamwork to win through this particular apocalypse and discover if the ending is a predictably bleak or a predictably hopeful one.