Welcome to the Left 4 Dead Thread! In this OP we are going to look at what some of the top industry insiders are saying about Left 4 Dead.
(Disclaimer: I searched for previous threads, and found one but it was pretty weak.)
Professor Wikipedia will now explain some of the basics:
Left 4 Dead
is an upcoming multiplayer co-operative survival horror
game by Turtle Rock Studios
and Valve Corporation
(a collaboration that has previously produced Counter-Strike: Condition Zero
, as well as maps and the official bot for Valve's Counter-Strike: Source
). The expected release date for Left 4 Dead
is early 2008.
The game has been built using Valve's Source engine
The game was first revealed in the Christmas 2006 publication of PC Gamer UK
with a six-page article describing a playthrough at Valve's headquarters.
The game was first playable at the Showdown 2007 LAN in San Jose
. It was also playable from August 2
to August 5
at QuakeCon 2007
. A Valve booth allowed a team of 4 survivors to play against AI controlled bots as well as 2 guest developers from Turtle Rock Studios
. However, the general public was only allowed to play as the four survivors.
The basic idea is that a team of four humans (the survivors) attempts to go from point A to point B. Along this linear path they will encounter the infected (not the survivors) and will be slaughtered mercilessly. Both sides can be controlled by players, however if any side is down a man (or four) it will be controlled by the AI.
The AI is quite advanced (according to top research press releases) and works like this:
The AI also features a dynamic system for game drama, pacing and difficulty called the "director". Instead of fixed spawn points
for enemies, the AI director places enemies in different positions, creating a new experience each time. It will also balance action and moments of tense calm. 
When the AI Director feels that players have been facing a particularly intense battle it will slow down the tide of enemies. After a sufficient lull of action the director will send more enemies to increase the drama again.
Sounds pretty exciting I'd say. The game will have a few different locales, but primarily we have seen Urban areas. It is also worth noting that while playing as the infected, you will have a choice of quite a few different types of "Boss" monsters that will wreck the survivors shit quite expertly.
UPDATE: It appears that the Xbox 360 version will also feature split screen play. To the extent featurewise I think is still unknown, but it should be safe to assume for co-op at least.
So you get the general idea of Left 4 Dead, but no OP is complete without improperly sized vague screenshots. Let's Watch:
(Warning, The camera feels the need to randomly look at the players and not the game, I will never understand that. Also 2 commercials play before the video).
TURTLEROCK AQUIRED BY VALVE
Here is the short synopsis from Kotaku
"We have been seeing very strong growth with Steam and Source, our content distribution and development platforms, up over 150% over the last 12 months. Given our expectations for Left 4 Dead and our long-standing relationships with members of the Turtle Rock team, this was an easy decision. It also gives us a base from which to expand our development activities in the Los Angeles area," said Gabe Newell, president of Valve.
"Left 4 Dead fills a long-standing demand gamers have had for a coop first-person action experience, and it will also help Valve's expansion into the console market," added Doug Lombardi, Valve's VP of marketing.
"Valve has had great success bringing in projects and teams such as Team Fortress and Portal. As I spent time working and talking with the creators of those products over the past several years, it became clear that this was the right next step for myself, my colleagues at Turtle Rock, our customers, and our products," said Michael Booth, founder and CEO of Turtle Rock Studios. "We are excited to be a part of such a visionary and forward-thinking company."
So, I'd say we're all up to speed for the most part. The release date is being reported everywhere as November 4th. The game will be available on Steam (PC) and for the Xbox 360 playable over LIVE.