A good game, but also a boring one
The game has 4 players playing a campaign through 4 "scenes". Well, thats really a great idea, but there isnt a story. You pretty much go from point A to point B, but for no obvious reason. In a zombie world, you have to escape, but there is no indication of how and who is going to rescue you.
There is a single player version of the campaign, and there is another game mode, versus mode.
In versus mode, you pretty much take the role of either the survivors or the stronger zombies. Often you get heavy amounts of lag, because you dont know if the server steam chooses is in your area or not. You also get grouped with newbies, who often dont know how to play.
While the concepts in Left 4 Dead are very good, there is definitely a poor execution. This in no way is a Team Fortress 2 or Counter Strike Source killer. For $50, it will pass by in a couple of weeks.
The graphics are very nice, with my 8800gt cooled by an Arctic cooling S1, it runs super smooth at 1680*1050. However, there are numerous bugs with nvidia cards, and some can cause major crashes. Processor bugs are also very apparent, you sometimes have to set your processor affinity to 1 cpu to not get slowdown and major hitches.
Aside from the issues I have stated, this is a good game, but its nothing like a good zombie game should be. There is no story, and the online is not as smooth as the other competitors such as TF2 and CSS. Wait till it drops in price before you pick this one up.