That's not to say there aren't moments of tension. But while I'll make a comparison to Aliens vs. Predators later on in this preview, Versus mode is simply too much of a blast to play to sustain any sense of real dread. In that respect, it's got more in common with Team Fortress 2 than something like Counter-Strike.

When the round ends--either with the humans reaching the room, or being decimated--the teams switch sides, playing the same map but as the other race. The team that carries the "ball" the furthest as the human side wins.

From the human perspective, the objective is identical to the co-op mode. But playing from the Infected side, everything changes dramatically.

As a zombie, you begin the round--and every subsequent spawn--directly on top of the humans. Unfortunately, you can't hit them yet--your first objective is to reach a place on the map where no human can see you. You are basically invisible in this preparatory mode, able to walk through doorways and quickly position yourself for an optimal spawn. Later on, as the humans venture further into the level, the fact that you "spawn" directly on top of them allows for a very quick turn-around, keeping the action flowing despite the 20-30 second respawn timer.

After leaving the ghost-spawn mode and coming alive, you'll see your human targets clearly outlined through the level architecture, as if using a Counter-Strike wallhack. At this point, it's all about finding the right time to attack. Brazen charges into a coordinate team of humans inevitably lead to instant defeat. A good zombie is a smart one, finding just the right time to make prey of the players. And though the primary goal is to stop the humans, you are ranked within your group of Infected based on the highest damage caused, so maximizing your individual effectiveness will also be part of the competition.

Playing as the Infected, you'll have far more abilities at your command than the average zombie. Most importantly, you can climb up pipes and other ladders, allowing for surprising ambushes as you drop down from above. Paw-print markings are scattered up and down the length of the ladders, easily marking where you can climb.

Other than that, the gameplay is largely dependent on which of the four Infected classes you are playing as.

The Hunter was probably my favorite. An agile monster, playing as the Hunter is a bit like playing as the Alien in an Aliens vs. Predator game. The idea here is to skulk in the shadows, leaping out to attack players when they are most vulnerable. To accomplish the pounce, Hunters must first charge up a circular meter around the targeting reticle, and then trigger the attack. After making contact with a human, the camera switches to third person as your Hunter pins him to the ground, slashing away at the poor sap.

The Smoker is even sneakier. This Infected uses its enormously long tongue to capture humans and drag them towards it, slowly strangling them to death. This class probably produced the most comedic moments. Lashing onto an unsuspecting human and dragging him or her into the middle of a horde of zombies was perfectly sadistic.

Adding to the Smoker's potency is the reason for its namesake--when damaged, it leaves a thick haze of smoke. I know from experience that trying to fight off dozens of zombies in the middle of this smoke is a recipe for disaster, so even in death, you're screwing over the other team.

The Boomer has a similarly obnoxious self-defense mechanism. A hugely fat slob of an Infected, really the primary way of causing damage as the Boomer is to get right up into the middle of a group of humans. Being such a large target, you won't last long, but the explosion of poison when you die will not only do damage to the humans, but also will blind them for a significant amount of time.

You also have a long-distance vomit attack as the Boomer. In one round I climbed my way on top of a building, positioning myself just above a doorway where the humans were emptying out. As they fought the AI zombies cruising in from their front, I blew my vomit all over their heads from above, then lept down into the middle of them, exploding in a glorious sacrifice.

The Tank is, well, self-descriptive. A massive, hulking beast, playing as the Tank makes you even more of a target than the Boomer. The second you are spotted, the humans lock on, blasting away.Of course, you can take a lot of hits--and dish out some serious punishment. Tanks only spawn every so often, however, so you won't always get to go on a rampage--but when you do, it's a great moment.

Overall, Versus impressed me more than I was expecting. Valve has really tuned the mode to make sense from a competitive standpoint, and the elements of comedy, anticipation, and fear are wonderfully mixed.

Versus also taught me the true meaning of Left 4 Dead.

The moment of education came as I spotted my teammate in trouble, an enemy Tank zombie wailing away at him. I clearly didn't have the time to take him out with my rifle, and more zombies were charging in the distance. I pulled out a Molotov cocktail in desperation, hesitating for a moment before hurling it at the Tank--and directly on the face of my friend.

With smart, player-controlled zombies out there, you can't depend on any breaks. It's your ass on the line, and it may not be worth climbing back down that ladder to save your buddy.

Sometimes, someone's gonna have to be left for dead.

Left 4 Dead arrives on PC and Xbox 360 November 18, with a downloadable demo due roughly two weeks before.