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.