Left 4 Dead at its core is a fairly simple game. You are a group of four survivors of the zombie apocalypse. You and your friends are immune to the virus that has overcome a majority of the population but you are still trapped in the middle of zombie hell. Your objective is to get from point A to point B through hordes of the undead with at least one person still alive and mobile enough to shut the safe house door or hop onto the rescue vehicle at the end.
To be a bit more elaborate, there are four "movie" campaigns which you can choose from when you create a new game. You choose your difficulty, invite your friends (or use computer controlled players) and the level starts. You have to fight through five sections of each movie campaign before it is complete. The first four are comprised mostly of moving through till you arrive at the next safe house, but the fifth and final scenario is always instead a situation where you must bunker down and defend against waves of zombies and super-zombies until the rescue vehicle is ready to leave or arrives to pick you up. Like an intense and undead version of tower defense.
There are multiple types of zombies as well. On top of your everyday "common infected", there are Boomers (fat zombies that spit or explode on you, causing a horde of common infected to come running), Hunters (fast and elusive zombies that can jump a great distance and pin you down) and Smokers (the most annoying of the special zombies as it can grab any of the survivors from a great distance and pull them away from the group). In addition to these "special zombies", there are what I like to call the "super-duper special zombies" of which there are usually only one per level section. The Tank is a huge muscular looking undead that takes an incredible amount of firepower to bring down and almost always incapacitates at least one of your buddies (but never me because I run and scream like a girl instead of fighting back). Also, there is the Witch which is probably the most disturbing and scary of all the zombies in the game. She will be found randomly in each level and can be located by the horror film music and sobbing that comes through your speakers as you get closer and closer to her location. If you shut off your flashlight and sneak by you can sometimes get away without a fight, but startle her and she will clothesline a couple of you into oblivion.
It is tough to be too opinionated either way here. The Source engine still looks similar to how it did when it was first released five years ago and has certainly aged a bit. That being said, the graphics are still acceptable and the art direction (as always with Valve) is very good. All the models look good, the environments are appropriate and detailed and the game seems to run well on lower end or older systems. If you're one of those folks who is all about form over function and just wants PC games that show off your stupid uber-PC you bought with multicolor-LED lit fans and a GeForce 69000GTXBUQa55-b, this isn't the game for you. Otherwise it does the job just fine.
This is where Left 4 Dead really shines. What could be more important than sound in a horror game? All the zombies have distinct screams. The common infected snarl, the Hunter screams, the Boomer gurgles, the Smoker hacks, the Tank growls and the Witch sobs and wails as she beats the piss out of your group. The eerie music is enough to make you shiver and wonder whats coming next and just understated enough that you might not even notice the effect it's having. The music ramps up and gets intense when a Tank appears or a horde begins to rush and gets slightly louder and scarier as you get closer and closer to the Witch in each level. This is a game that for all intents and purposes should never, ever, ever be played with the sound off. You will be gimping your ability to hear what is coming next and you would be missing the exciting and intense effect that it has on everything you do and everywhere you go.
On top of all the zombie and environmental effects, the survivors themselves have a large number of lines that they will spout off during the game. Most are useful information letting you and your group know that a special zombie is nearby or that you should use a medkit. A few are simply to help give the characters a personality and to give you a laugh. Perhaps my favorite was when I stepped into an elevator and took it up to get away from a giant zombie horde. Finally a calm quiet moment after a flurry of activity when Francis the biker looked at me and said "Who beefed?" Zoey, the female survivor I was playing at the time, apologized for her infraction. Priceless.
The feel of the game and its controls are thankfully just as good as any FPS and feels similar to the other Source engine games. Weapons are limited to a couple automatic machine guns, a couple shotguns, a sniper rifle, an occasional mouted gatling gun and a couple different types of grenades. While the selection of weapons is sparse compared to your average shooter, they are all distinct and offer certain advantages or are used in certain ways to cope with the zombie rush. It certainly makes sense to have your friends spread out what they equip so that you get a variety of all the weapons as the sniper rifle is great at very long range, the automatic weapons are great at medium range and the shotgun excels at very close range when the horde has managed to get right on top of you.
Grenades come in two varieties: The Molotov Cocktail and the Pipe Bomb. Unfortunately here things are a bit imbalanced as the pipe bomb is considerably more useful and effective. All survivors also get a pistol (or two) with unlimited ammo in case their main weapon runs out and each survivor can stun and push away zombies with a melee attack. Tactical use of this ability is critical to being succesful on higher difficulty levels where friendly fire does a large amount of damage and pushing zombies away is the only way to help your friends get a shot off without hitting you.
Overall the gameplay has a great feel and flows very well. There is a lot of tactics based around how you handle multiple zombies as the common infected swarm you as well as how you handle the special zombies. Teamwork is essential as one or two people can easily become overwhelmed and will need to be saved by the rest of their group. Honestly I cannot ever see playing on any difficulty below Advanced as the game thrives on putting you into desperate feeling situations that make you feel like you have truly accomplished something every time you get to the next safe house and lock your friends out so that they die and you complete the level alone.
Realistically, this game is only multiplayer. The computer controlled bots are not too bad but nothing can ever replace playing with real human beings. This is easily the best co-op shooter I have ever played (sorry Gears of War, I still love you). Additionally, there is a versus mode that puts four additional players in the role of the special zombies and allows you to try and stop the survivors from reaching their objective. While it is a nice bonus and a little bit of a change as you get to be the hunter instead of the hunted, it is still essentially the same game.
There is no doubt that Left 4 Dead is fun. If the game even sounds remotely appealling to you and you have two or three friends who would be interested in playing with you, you will very well have a blast. That being said, I went over most of the positives above (great gameplay, great sound, great art direction and animations) so I will go over the one big negative right here: variety. Even after only a week of playing, I have been through every mode (campaign with bots, campaign with people, versus) and I have beaten every movie campaign at least twice. There are still a number of achievements I have to work towards and I would love to try and beat all the campaigns on expert but it is still a bit dissapointing. How many times can you play through the same levels fighting the same few zombies with the same two weapons? I am still having fun but I could see it being an issue more and more as I continue to play. Perhaps $50 is a bit steep for a game that is essentially not that chockful of content but it is hard to complain when the quality is so high and when Valve is known for releasing free updates (and they have mentioned more campaigns and zombies being added during updates which are free for PC users).
The bottom line is that this is a great game and perhaps the most fun I have had with a co-op shooter ever. I will continue to play and enjoy myself and I hope that Valve is quick with releasing additional content to keep a great game fresh.