There was little doubt that Valve's only game scheduled for release this year would generate plenty of interested at E3. But after spending nearly an hour with the game, it became clear that Left 4 Dead was one of the most exciting titles at the show this year, one that looks to continue Valve's tremendous success with 2007's Orange Box.

Left 4 Dead was developed by Turtle Rock Studios, which was acquired by Valve earlier this year. The first-person shooter game follows four survivors of a massive zombie epidemic who must fight their way through different environments. Left 4 Dead is a multiplayer cooperative game that allows gamers to player as the four survivors as well as some of the zombies. The game also has five different chapters or maps.

During the preview session, Valve invited four media members (including this writer) to play the game's "Hospital" a chapter. The demo started with the four playable characters (I played as Louis) on a rooftop at night and forces them to travel through an extensive urban environment to reach a safe zone. Valve's Chet Faliszek, the write behind Left 4 Dead, provided an overview of the game and guided us along the way. The controls were based on Half-Life 2, so they were easy to pick up.

On the rooftop, we were given a few first-tier weapons, including an Uzi, a pump-action shotgun and a standard handgun that never runs out of ammo but isn't much good if you're being swarmed by the undead. I grabbed the shotgun and set off with the rest of the group down the stairwell of the building, but it didn't take long for the action to start - zombies began charging up the stairs as soon as I opened the door.

The first thing I noticed about the game was the friendly fire feature; if you're standing in the line of fire of your teammates, you'll take damage and your character will yell something along the line of "Will you PLEASE stop shooting me!" Faliszek said playable characters won't take the same amount of damage from teammates' weapons as the zombies, but players still have to be careful. "The friendly fire is for creating that feeling of complete chaos," Faliszek said. "If you're teammate only has a few points of health left and you pop him with a shotgun, he'll die."

On the other hand, players can pick up health kits and pain medication (which looks like a bottle of aspirin) and use them or give them to wounded teammates, who show up on screen in a white silhouette and a red exclamation point. The trick is, applying health kit bandages take a few second and make you vulnerable. As a result, players need to be careful about when and where they choose to heal because picking the wrong time or location will be fatal. And finding a free moment when you're not under attack is a lot harder that I expected.

That's one of the truly great aspects of Left 4 Dead: you never feel completely safe. Zombies attack from every direction. Even after you progressed through a point on the map, zombies will creep up from behind and swarm you, forcing you to bash the zombies with melee attacks. If a four-player squad doesn't work together and communicate, then the game won't last very long. Someone always needs to be watching the squad's blindside because you can be sure zombies will bust out of the shadows at some point.

While working our way through narrow, claustrophobic corridors of the apartment building and blasting zombies in close, shadowy quarters, we came across some new items, including some Molotov cocktails. The flammable weapons are key because zombies will charge through the flames with complete disregard to their own safety, which creates a lot of damage. Of course, if you're not careful about where you're tossing the Molotov cocktails, you could cause major damage to yourself and your teammates.

After reaching the ground level of the apartment building and exiting to an alley, we began to hear some rather disturbing sounds - doors banging and gruesome zombie moans. Soon enough, we encountered new types of zombies beyond the standard fast-moving, vicious infected. First up was the Boomer, a fat, slumbering zombie that fires projectile green vomit (think "The Exorcist") that sticks to players that inhibits their view and also attracts other nearby zombies like shark chum.

There's also the Smoker (no, not like "Waterworld"). This kind of zombie attacks with a long, slimy tongue that acts like a boa constrictor. Smokers love to hide above the survivors and snatch a player at the rear of the squad while the other three aren't, lifting him or her up and using its tongue as a noose. If a Smoker grabs hold of a player, he or she will show up in the white silhouette and yell for help. But you won't have a lot of time before a Smoker strangles the life out of your teammate. And if you attack a Smoker, the zombie will create a cloud of black smoke like a squid, which creates even more panic because you can't be sure if you're shooting the Smoker or your trapped teammate.

Next up is the Hunter, which is similar to the fast zombies in Half-Life 2. These zombies are extremely quick and hard to target as they jump out at unsuspecting players and leap across the map, avoiding gunfire. If a Hunter leaps on a player, it can incapacitate him or her by pouncing on the player with its lethal claws. The only way to survive a Hunter attack is for a teammate to knock the zombie off of you. The good news is that Hunters are more fragile than other zombies and can be taken out with a few shots. The bad news is they are extremely hard to hit.

The most interesting and unique foe is probably the Witch, which also happen to be the only non-playable type of zombie for multiplayer. The Witch resembles a pale white little girl and can be found huddled and whimpering in a dark corner at various points on a map. Now here's the catch: you can completely avoid the Witch but only if you don't create any significant noise or shine a light on her. If you do happen to point your flashlight in her direction, the Witch will begin screaming and launch a devastating, blood-letting attack on the nearest player. The Witch is arguably the most powerful zombie.

There's also the Tank, which is a large, muscular foe that can stomp and pummel the survivors like a zombie version of the Hulk. The Tanks can sustain quite a bit of damage before falling and require carefully executed teamwork to defeat. Players can usually hear the thumping sounds of the Tank lurking before it attacks, but once it discovers the players, it will become enraged and begin throwing objects like cars and concrete slabs at players.

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