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Back in early 2007, FASA Studios released “Shadowrun,” a cyberpunk-and-magic first-person shooter for the Xbox 360 and the PC that featured no single-player mode beyond a handful of training missions. Angry gamers declared it a ripoff because it was a multiplayer-only title and they refused to pay full price for “half a game.”

If anyone’s leveling the same complaints about Valve Software’s “Left 4 Dead” (rated M, $60 on Xbox 360, $50 on PC), they’ve been drowned out by the squeals of delight from fans of 2008’s most balanced, finely tuned multiplayer shooter. You can play “Left 4 Dead” by yourself, but no one will want to for long.

As the number in the title suggests, it’s best played with three of your most trusted gaming buddies. A foursome of B-movie archetypes (college student, office worker, grizzled Vietnam vet and tattooed biker dude) fights its way through four appropriately styled scenarios, gunning down hordes of zombies en route to an evacuation point, where an epic standoff occurs before help arrives. The foursome, known as the survivors, are among the few people immune to whatever caused a massive zombie apocalypse. In other words, most of the rest of the world wants to tear them apart. Splitting up is a bad idea. And that’s pretty much the whole plot.

The zombies in “Left 4 Dead” don’t shamble after you like it’s “Night of the Living Dead.” They’re from the “28 Days Later” and “I Am Legend” school. They’re fast and agile, and they’ve only one goal in mind: Slaughter survivors.

In addition to run-of-the-mill zombies, you’ll have to watch out for several special varieties of undead. Each has a signature move it uses to incapacitate or harass survivors. The morbidly obese boomers, for example, vomit on their opponents, temporarily blinding them. Better yet, the vomit attracts a horde of regular infected. Not only can survivors not see, they’re the zombie equivalent of a $250 HDTV on Black Friday.

As far as the special infected go, the star of the game, by far, is the witch. When you stumble across one, you’ll know it right away, as the first thing you hear is soft sobbing. As you get closer, her signature, creepy music kicks in.

The thing is, the witch just wants to be left alone to cry. If you give her enough space, she’ll ignore you entirely; you’ll want to turn off your flashlights and sneak by. But if disturbed, she’ll focus all her energy on the survivor who interrupted her, knocking him down and making short work of him if teammates don’t come to the rescue.

Unlike “Halo 3,” which shoehorned crowded four-player co-op into what felt like a game designed for one or two players, “Left 4 Dead” was clearly a four-player title from the get-go. If you can’t find enough friends to play with, the computer will take over for the rest of your crew.

Split-screen play on the 360 allows two gamers to play on one console, but the real fun lies online, where four survivors can play through the scenarios. A separate, versus mode hits the multiplayer sweet spot, letting two teams of four square off. Each team plays through a level twice ” once as survivors, then as special infected trying to stop the other team. (The witch is the only computer-controlled special infected, but trying to lure hapless survivors into startling her is a fun meta-game all by itself.) Teams are awarded points based on their performance as survivors.

Where “Left 4 Dead” shines is how it rewards you for helping your teammates and punishes you for trying to go it alone. Too many allegedly team-based shooters simply devolve into four or eight teammates each trying to play “Rambo,” ignoring attempts at team play and racing for the weapon of their choice. In “Left 4 Dead,” though, solo gamers who desert the flock will be incapacitated and begging for rescue in no time at all, and there are plenty of weapons for everyone. Furthermore, the game’s different-every-time structure means that power-ups and ammo may not be where you think they are.

While the game’s short on plot, what little writing there is is outstanding. The scrawled graffiti and cheesy one-liners from survivors break the tension perfectly. My favorite so far is office worker Louis’ “Stay positive, guys. I’ve got a good feeling about this!” just before a swarm of zombies hit.

“Left 4 Dead” might not be for everyone. With the heavy focus on multiplayer, it helps to have a robust roster of buddies with which to play. I played my Xbox 360 copy online with real-life friends and assorted strangers, and the real-life friends by far won out. (For starters, no one ditched the game halfway through.)

If you’ve got a decent gaming PC, you’ll want to lean toward that version. Valve is poised to announce additional content for both platforms, but the inevitable fan-created levels and modifications should wow the mouse-and-keyboard crowd. That said, the less precise aiming of console controllers doesn’t come into play quite as much in “Left 4 Dead” as other twitch shooters. There are simply so many infected to shoot and so much going on at any given moment that you don’t have a lot of time to aim precisely, anyway.

More than three years after the release of the 360 kicked off this generation of gaming consoles, we finally have a multiplayer-only shooter that few are dissing as “half a game.” (It’s a ridiculous criticism, anyway, when you consider how few single-player-only games are subjected to the same knock.) If a game’s good, it’s worth your money. If you crave a multiplayer shooter that’ll keep you at the edge of your seat while discouraging many common online gaming pet peeves, you can’t do much better than “Left 4 Dead.”