This is why I love Valve games, original and innovative, coop zombie killing? its a blast :)
Left 4 Dead (L4D) is a great fun and innovative coop zombie fest, very addictive and with surprising value considering it only has four short campaigns. Valve have done it again with L4D, its an original and fun game which shows us that coop can and should be done on the PC. However considering it is pretty short you might want to wait for the price to come down a bit, ideally as a full game it ought to of had a couple more campaigns. Its probably worth noting that L4D is controversial in the gaming community, many gamers feel its too short for the price and are miffed that valve haven't supported the game in the same way they supported Team Fortress 2, plus some see the imminent release of L4D2 as a kick in the teeth. That said you've got to weigh the game on its merits and I think it deserves a score of 9 for its innovative contributions to PC gaming alone.
Graphics:
L4D uses the source engine so its lightweight and looks pretty good, however don't expect to be wowed by the graphics the source engine is starting to get a little on the venerable side, basically if you've played any of the other source games then the graphics will feel very familiar.
The maps and modeling are very well done, its polished and immersible all though, nothing looks out of place. Being a zombie game it does all take place in the dark or rather dim light, it works well though, the source engine is good for this sort of lighting plus you have a torch fitted to your guns which can be turned on of off but doesn't run out.
On the whole its what you would expect, leached colours, lots of blood etc... plus trashed buildings and cars.
Sound:
Good voice acting goes a long way towards a good game and L4D doesn't disappoint although it is a little sparse, the four playable survivors each have a repertoire of spoken emotes, controlled by the player in a similar manner to Counter strike. Plus there is scripted speech from each character as you progress through the maps. The zombie noises are good enough, pretty much what you'd expect, weapon fire is also ok but nothing stands out as excellent. The music is apt and does the job, there's not a great variety but its moody and makes for good background noise.
Game structure:
L4D comes as four campaigns, each campaign has the same theme, you play one of four survivors in a zombie infected area and need to get to an evacuation point. Each campaign features a different evac method, Helicopter, boat, armoured car, and C130 airplane. Basically each campaign is split into sections, punctuated by safe houses where you can get guns, ammo and medi kits (and load the next area) - which will also be spread around the maps in various places, usually slightly off the main "path".
You can play through each of the campaigns in single player mode, with the AI controlling your companion survivors, this works well enough and is worth doing once to familiarise yourself with the game.
However L4D is primarily a multiplayer game, and this is where it really shines; there are three online game modes, "campaign" - where you simply play through the campaigns in 4 player coop, "versus" - the survivors must work their way through the maps as normal but upto four human controlled boss zombies will be trying to stop them in addition to the usual hordes, and "survival" - unlimited zombies, survive as long as you can (then die). Versus and survival are hardcore so don't play these until you have at least 15 of the normal campaign games under your belt. Then of course there is advanced and expert mode if you're feeling really frisky.
Gameplay:
When I first fired up L4D I must confess I was a little disappointed, it feels a bit basic and familiar, also its very short, you can play though the campaigns in a few hours. Its also a little on the repetitive side but blasting zombies never really gets old ;). You have to persevere though because once you get into L4D it is a very addictive game, a few hours gaming rapidly turns into 6 hours, then 12 hours :) the coop element really makes the game, especially when you get some players together who are good sports and teamwork well. A definite bonus is the fact that valve have left the splitscreen code in the game from the xbox, unofficial unfortunately, but with just a little tweaking and hacking it works well, i've played though a campaign with a friend and it was worth the effort setting up.
What keeps the game fresh is the "AI director" which is basically reactive spawning, the zombies, and boss zombies, will be in different places each time you play. Plus if you're doing really well the AI director steps up the pace and throws more zombies at you, or if you are struggling it will back off a little. This also applies to pickups such as health (med packs and pills), grenades (pipebombs and molotovs), and guns; if you're doing well there will be less and harder to find, if you're doing badly there will be more.
Most of what you will be shooting are the standard "infected", basically your average rage zombie type, they will be docile and mill around or lean against walls until they notice you are there, then they go nuts are sprint at you really fast. They are placed around the map, usually in pretty much the same places, in addition there are a large number of spawn points where a "horde" of zombies will spawn and all run at you, these are more random, where they are and how many zombies they spit out and when. It works pretty well thanks to the AI director. Most of the time these standard infected are pretty easy to handle, you can take a bunch down with a single shotgun blast and one or two bullets will normally do the trick too. they don't do much damage and you're only really at risk if you are absolutely surrounded by dozens and your health is low - I think each time they hit you they take your health down by 1-2 points so you have to get slapped plenty before you go down.
Then there are also a few "boss" zombie types, you'll become familiar with them very quickly so i wont bother to elaborate here, suffice to say they shake up the action well and are interesting to play in versus mode.
Valve have also added in their hallmark "Achievements" which gives the game a little more longevity, basically they are medals they you earn for completing certain actions in game, e.g. surviving a campaign, killing x number zombies, killing zombies in a certain way etc..
Each of the campaigns culminates at the rescue zone, when you call on the radio for help you have about 5 minutes of being rushed by hundreds of zombies attracted by some noisy element of your escape e.g. the fuel pump filling up the C130. Right at the end when your rescue arrives there will be a final push of zombies, this is where you are most likely to die because you have to leave your stronghold and make it to the vehicle - if the others get on the vehicle and you go down on the way then you will be... left 4 dead.