The day is here: Valve has shipped another game.

At this point, you've heard us go on and on about this one. Yes, Left 4 Dead is a great game. It's a fresh co-op experience, presented in unique movie-sized campaigns. If it sounds like you'd enjoy that kind of thing--or you liked the demo--it's an easy purchase.

But there is that pesky question of value, along with the possibility of hidden flaws. And so we trudged down to Valve HQ to review the full package ahead of time, playing countless hours of the game to answer a few necessary questions.

Namely: What exactly are we getting with Left 4 Dead? Sure, the demo levels are largely indicative of the full game, but how much game is there? Is this something that will get old after the first day? And what about this Versus Mode? Is it an after-thought, or a full-fledged component? Read on for our collective thoughts.

Breckon's Take
It's actually very easy to quantify just how replayable Left 4 Dead is, in the same way that one can identify an infectious disease.

Because that's what playing Left 4 Dead for the first time feels like--the beginning of a terrible affliction. We played the game for two straight days at Valve, only occasionally surfacing for a gasp of fresh snacks. We played so much Left 4 Dead that it made us all physically ill. We came home thoroughly infected, bed-ridden and moaning like the undead.

And the most common phrase going around our chat channel? "I wish I could play more right now."

Weeks later, I've been playing the demo--a mere two stages of the full game's 20--almost every day. It's safe to say that Left 4 Dead doesn't quickly get old.

We've talked endlessly about the AI Director, the computerized game master that randomizes spawns and controls when and where your team is attacked. In truth, this system only serves to keep you constantly looking over your shoulder. And while that certainly adds to the suspense, it is only one part of why Left 4 Dead is such an exhilarating good time.

This is a game about little touches--the unpredictable scenes of horror and hilarity. The way zombies can slowly break down doors. The way encounters with the massive Tank enemies devolve into Looney Toons-esque chases. The way you feel when the safe room is finally in sight, and a zombie horde suddenly rushes out in front of it.

Even without the random elements, blasting zombies in Left 4 Dead is just plain fun. This is a well-tuned, very responsive shooter, with a solid core. The minimalist approach to the weapons works well, offering just enough rifles and grenades without devolving into a game of Quake. And the wonderful melee attack is particularly notable, factoring heavily into gameplay by allowing for last-second escapes and desperate flailing.

The levels themselves, while technically static, provide enough of a variety that the game rarely feels stale. Valve has covered all the bases here, giving us scenarios that range from a last stand in an abandoned farm house, to a rooftop escape via helicopter. The landscape often changes drastically within the chapters themselves. Over the course of a single campaign, you'll find your group of survivors moving from the streets, through a sewer, and into a hospital--each chapter always ending in a harrowing rescue sequence.

Outside of the oft-described co-op experience, there is also a great challenge to face in Left 4 Dead. Playing the game on Expert mode can be a grind, something that gamers have already discovered with the demo. But working through these challenges with a group of three friends is far more satisfying than breezing through the game on Easy. After finally crushing that last Tank and jumping into the safety of the rescue boat, you get the same satisfaction of successful teamwork that can be found in a World of Warcraft raid--but with a fraction of the time spent, and a lot more headshots.

But that's enough about the co-op campaigns. While that component alone makes Left 4 Dead a worthy effort, I think Versus Mode is going to catch a lot of people by surprise. It is surprisingly fun to play on the Infected side--or as I like to call it, "Team Griefers."

Perhaps sensing that all cooperation and no competitive play makes for a dull game, Valve has created a mode entirely based on griefing other players, albeit cooperatively. The setup is simple: the two teams take turns attempting to make it further through a level than the other, alternating between zombie and human. The team that gets further as the humans wins--meaning the winner is often determined by the teamwork of the Infected side. Playing as one of four boss Infected, you'll have to carefully time attacks with your zombie friends in order to maximize the chaos.

Grasping players with a 40-foot long tongue and yanking them backwards, or pinning them to the ground as zombies munch on their feet, or vomiting on their faces--all of these delightfully annoying attacks define Infected gameplay. Picking off stragglers becomes the name of the game, leading to some very personal vendettas. In a LAN setting, the screams of your victims becomes a delightful reward to a clever ambush. When playing online, enabling all-talk voice chat will be a must.

One downside to Versus is that players can't simply choose which Infected they wish to play as--the game is constantly randomizing your "class" and instantly spawning you. So while your favorite Infected to play as may be the Boomer, you could get stuck playing as the Smoker several times in a row. It's a minor gripe, and one that is rendered mostly irrelevant; each class presents its own challenges, and learning to exploit their strengths can be a rewarding goal.

Valve has done something clever by ensuring that going it alone, in either component, will almost always lead to failure. Those players who wander off into the fray to play Rambo, or attack a coordinated team of humans alone, will more often than not be met with a quick death. That is the real genius of this co-op title: it forces even the most competitive jerk to play nice with his team, to relax and enjoy the game the way it was designed to be played.

Of course, your experience will always vary based on the quality of your group. But I'll let Chris touch on that.

Faylor's Take
Make no mistake, Left 4 Dead is easily one of the year's best multiplayer games. I'd even go so far as to say it's one of the best multiplayer games I've ever played.

You see, unlike some other co-op games, Left 4 Dead doesn't force teamwork to get through some arbitrary puzzle or navigate some silly level. Simply put, if you want to live, to make it through the endless horde of zombies, you need to communicate, to work together. There's no other choice. Especially on the harder difficulty settings, which is where the game really starts to shine.

If just one person falls in combat, the whole team is screwed. Between the long-reaching and incapacitating tongue of a Smoker, the long-range tackles of a Hunter and the zombie-attracting vomit of a Boomer, you need four people to stay together, to watch out for one another. Without that fourth person, there's no one to help when the shit hits the fan.

Not if, when, because, trust me, the shit does hit the fan, especially when playing aginst a team of human-controlled zombies. For the most part, that worst-case scenario is pretty much a sure thing, but because of that AI director, it's different every time.

You never really know. Hey, this time, you might get lucky.

The funny thing is, if nothing happens, there's a decent chance you'll make something happen. After Steve and Blake were lost to the horde, Nick and I booked it to the safe room. It was a fierce struggle, and Nick almost didn't make it. In fact, after I made it into the room, I had to go back and help Nick work through a wave of zombies that had him pinned.

And just as we were about to make it, mere feet before he was about to enter the door, I was inspired to shoot him in the face. Don't ask me why, but watching him fall just steps away from safety as I slammed the safe room door in his face, well, I'm still laughing about it. And I'm pretty sure Nick's still pissed about it.

Read on for more thoughts from Faylor, along with insight from Blake and Steve.