If you're after four letters that tell you what a big deal the Halo franchise is, how about these: ODST. Try them out - only a series that's really put some big numbers on the board could follow them up with such a resolutely unsexy initialism. ODST sounds like a mid-western dairy farmers union, perhaps, or the name of a qualification you might need in order to operate a forklift truck. Both Bungie and Microsoft must be feeling pretty confident to let their favourite daughter go out on a Friday night dressed like that, then.
For those of you who don't spend your spare time forging personal-use Spartan armour out of old cereal boxes, or sketching complex political maps of Planet Harvest, ODST stands for Orbital Drop Shock Troops. They're futuristic super-commando types who plummet out of the sky in over-designed coffins prior to sending the Covenant to their graves, and after so long lurking in the fan fiction zone, they've finally stepped out of the Extended Universe and right into the starring role of the latest Halo game.
And while the exact status of that game remains in question - it comes on its own disk and is positively shiny with developer effort, but with that "3" in the title, it's always going to be judged as an expansion - it certainly kicks off with the practised grandeur of a company that's been doing this Halo stuff for quite a while now and knows how all the pieces work.
After a brief opening cut-scene that introduces your predictably gruff team-mates - you're the Rookie and you have to put up with the kind of friendly joshing from your squad which would have most people arranging an industrial tribunal - ODST injects you straight down through a gigantic battle raging in Earth's stratosphere, before crash-landing you into the city of New Mombassa, just after Master Chief left so explosively in the middle of Halo 2. Attack ships on fire indeed.
You wake up five hours later, with the city looking thoroughly stepped on, and from that point forwards, ODST splits in two: unfolding both as the Rookie explores the largely deserted midnight city, searching for the team-mates he's been separated from, as well as branching out into elaborate playable flashbacks from the perspectives of the rest of his squad whenever he finds a sign of their presence.
The flashback sections will be the most familiar to veterans of the series. The one we're shown may not have the most dazzling agenda - leaping into the role of ginger-haired hard-man Dutch, you start off by setting charges to blow up a bridge, which means that for the first few minutes, you're given the delightful task of following some way-pointers around - but it's Halo more or less as you know it: under a hazy afternoon sun, you've got team-mates fighting alongside you, and there's lots of chatter and wisecracking as you use the Spartan laser against the swarm of covenant troops trying to shell you from faraway Wraiths.
Rookie's mission, however, is something entirely different. Lost deep in the shattered city, the game unfolds in a beautifully-lit mess of buckled roads and malfunctioning street signs, while skyscrapers burn in the distance. It's a deserted and effortlessly mysterious environment, and with the action coming in the form of isolated encounters with small Covenant patrols, most of Rookie's mission is about puzzling things out - picking through the city, finding clues, and knitting together the pieces of a story which could very well turn out to be an inquest.
Bungie is describing ODST as a mystery, which sounds promising, and there are clear overtones of film noir, but you won't be walking the mean streets of New Mombassa entirely alone, as the enigmatic Superintendent is there beside you. An automating city-management computer, he's been watching your moves and wants to help, giving you a handy 3D map of the area with specific locations marked for you to investigate, and offering guidance whenever possible via New Mombassa's own video-screens.
In the early stages of the game such screens simply show you the way to your next objective and offer fairly comic pep talk, but it's exciting to imagine what a company like Bungie could do with such an unexpected companion, hopefully busting him out of the role of mere plot device and making him a crucial part of the story itself.
Whatever happens, it's probably a good thing that he's there, as a big part of the latest Halo is about reminding you that you aren't Master Chief anymore, and showing you what it's like to feel vulnerable. Not only is Rookie alone, but ODST can't jump as high or run as fast as the Spartans, and they don't have movement sensors, so you'll have to pick and choose your encounters rather than wading into every fight confident that you're a world-beater.
Bungie's even tweaked its famous health system once again to drive the point home, bringing back medipaks in the form of the city's health stations, and returning to something akin to the original Halo game's approach, with a small amount of rechargeable 'stamina' on top of a longer health bar which has to be replenished manually. On the plus side, however, new VISR display allows you a kind of night vision, while also differentiating enemy units from friends, and there are two ODST-specific weapons to screw around with: a silenced pistol, which can take off a grunt's head in one shot, even if it sounds like you're firing staples, and a silenced SMG.
The campaign is only half of any Halo, of course, and Bungie's also revealed a multiplayer mode called Firefight. Akin to Gears 2's Horde, it's a wave-based survival co-op game, supporting up to four players online or using System Link. Enemies attack in randomised rounds which build in intensity, and complication comes from the skulls system - different combinations of skulls becoming active as the game continues, inflicting a number of punishing conditions on you: maybe boosting the Covenant's health or improving their weapons, say, until, if you can last long enough, all of the skulls are in effect at once and the game becomes an exercise in high-score sadism.
With Bungie as control freakish as ever, the sequence the skulls fire in is fixed each time you play, but the developers are confident they've nailed the perfect arrangement, and given their commitment to playtesting, it's probably safe to let them have the benefit of the doubt. Playing Firefight on the show floor certainly reveals a meaty and highly challenging co-op game, in which teamwork - and often sticking fairly close together - is utterly essential for survival.
Taken as a whole, ODST is a fascinating prospect: sections of it suggest that it's business as normal, but other parts of it, where you're cut off from everybody and trading ballistic adventures for a purer form of urban exploration, hint at an entirely new side to such a well-travelled series. Lithe and mysterious where some found previous Halos to be a little bit windy, you've gone from galactic superhero to new boy, but that's unlikely to be the cause of too much disappointment.
Halo 3: ODST is due out for Xbox 360 on 22nd September.