Marcus Fenix's unruffled expression and gruff voice don't change much, whether he's offering curt condolences to a friend who's just lost a loved one or resolutely sawing away at the aorta of a giant worm from within its own chest cavity, waist-deep in the creature's blood.

In most narrative contexts, this would make him an unappealingly one-dimensional hero, but in Gears of War he works. Maybe it's because the game depicts a world in which humanity's prospects are so bleak and desperate that without the kind of firm bedrock that Fenix provides, you might be tempted to just pack it all in and give up.

Gears of War 2 is, of course, the follow-up to Epic Games' stunning third-person shooter Gears of War, in which humans fought against a relentless alien foe known as the Locust. The sequel picks up six months after the events of the first game. Fenix and the rest of Delta Squad, a band of super-soldiers similar to Marines (but with much, much thicker necks), are heroes for planting the Lightmass Bomb in the Locust-infested caverns deep below the ground. However, the mass explosion didn't quite eradicate the Horde as they had hoped. Instead, the enemy survived and regrouped, and as the new story begins, they've pushed the humans to the point of being able to muster only one final, desperate gesture.

The plan is to take the battle directly to the Horde itself with a daring attack targeting its Queen, while protecting the city of Jacinto -- one of the last bastions of humanity that hasn't been gutted, flattened, sunk or overrun with Locust. It's hard to guess how many humans are still alive at this point, but it can't be all that many.

As usual, the odds aren't looking good for Fenix and his three equally tree-like allies: long-time friend Dominic Santiago, the smart-ass Damon Baird, and the human juggernaut Augustus "Cole Train" Cole. Although supporting characters come and go, these four remain the nucleus like they did the first time around.

I spent a great deal of time with the original Gears of War in both its single-player and cooperative modes, so stepping into the second game felt quite comfortable.

Epic more or less perfected the "cover system" style of gameplay in Gears of War, which required a far more cautious and calculated strategy than the typical shooter mentality of running out with guns blazing and hoping that a few well-timed dodges would save you from enemy fire. As lead designer Cliff Bleszinski described in an excellent New Yorker piece, Gears of War is more like playing a game of paintball by seeking cover using whatever is available in the environment (in Gears' case, concrete barriers, doorways, burnt-out vehicles), and strategically moving forward while picking off enemies one by one.

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Wisely refraining from meddling with a good thing, Epic instead focused on a handful of subtle tweaks and tasteful new additions.

There's a new enemy called a Ticker -- picture those annoying galloping creatures that used to swarm up to you and claw you ... but with bombs strapped to their backs.

Remember Boomers -- those guys that would enthusiastically yell "Boooom!" before flattening you with a one-hit-death missile? Now they wield flamethrowers, Mulchers (a kind of rapid-fire Gatling gun) and a medieval-style flail and shield. Defeat any of these beasts, and you can equip their ?ber-weapons yourself and wreak some serious havoc. The flamethrower is particularly satisfying, for obvious reasons.

You can also grab the discarded shield and run with it. Sure, it slows you down, but it proves to be impenetrable to pretty much anything. I used it to great effect, on one occasion walking right up to a machine-gun nest while the nearly point-blank bullets ricocheted harmlessly off. You can also plant the shield in the ground and use it as portable cover. If there's no actual shield handy, you can always grab a fallen enemy and use it as a "meat shield" to absorb a few hits.

The distinctive crouch-and-run technique, the so-called "Roadie Run," is for the first time actually used in a puzzle-solving context, as is the chainsaw gun (to mow down cables and scenery).

Co-op mode has undergone some welcome refinements as well. It's still the Dom and Marcus show, with a mixture of side-by-side fighting and branching-path missions in which you're forced to split up. Often, though, you're paired with another computer-controlled character who can still heal you if you happen to go down. One of the most frustrating things about co-op in the original Gears was having to restart a checkpoint because a player died during one of the branching-path missions while cut off from the healing abilities of the other player. Gears of War 2 puts players into this situation far less frequently. Also, each person can select a separate difficulty level, allowing players of different skill levels to still work as a team.

Beyond co-op, the game offers a comprehensive set of eight different multiplayer modes, including new ones called Horde (where a team of players faces off against waves of increasingly challenging enemies) and Submission, a twisted take on capture-the-flag where the "flag" is actually a human character that the others must try to drag back to camp.

What truly makes Gears of War 2 so much of a triumph is that while the gameplay feels instantly familiar, situations don't feel like retreads. The tension-release pacing is superb; scenes shift seamlessly into the next with checkpoints updated and new orders being issued on the fly.

And more than in the first game, I found it a genuine pleasure to fight alongside my computer-controlled comrades. They would shout out hints about where enemies were hiding; they looked at each other when they talked instead of staring like mannequins; and when I got hurt they'd actually run over and heal me.

What's more, the world -- even while largely made up of the same greys and browns as most shooters seem to be -- still manages to be vibrant, often breathtaking. On one mission I emerged into a massive underground cavern, high ceilings bathed in a yellowish glow, waterfall cascading into a rippling lake below, and was struck by how beautiful a scene could be still rendered in such understated colors.

The world is a brutal one though, and the game doesn't let you forget it for long. Indeed, the unflinching portrayal of violence can get intense at times, and not just in an "eww, that's gross" way (although there is plenty of stuff that's over-the-top to the point of being cartoonish). One particularly harrowing scene at a Locust prisoner-of-war camp is an example of a different kind of intensity that I'm not going to forget any time soon.

Like in the first game, the ending of Gears of War 2 is open and a little unsatisfying. The finale (and subsequent blink-and-you'll-miss-it epilogue teaser after the credits roll) raises more questions than it puts to rest. I'm not adverse to more Gears of War games -- in fact, quite the opposite -- but I'll be interested to see where the story can possibly be taken. After all, humanity can only teeter on the brink of extinction for so long before epic declamations like "last remaining defense..." and "impossible odds..." start to lose their impact. I'm starting to crave some sort of closure, lest poor old Fenix comes back in Gears of War 10 for humanity's last, last, last stand -- six old men in a tent.

This review is based on a retail copy of the game provided by the publisher.

Get the first hour in Kyle Orland's Games for Lunch: Gears of War 2.