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.

You can read the entire article at Bit-Tech.