The year is 2552. Covenant forces control the city of New Mombasa. They are searching for something beneath its darkened streets. You are an Orbital Drop Shock Trooper. Your orders: stay alive, meet up with your scattered squad, and escape the embattled city.

• Fan favourite and Halo series stalwart Sergeant Avery Junior Johnson is a tough-as-nails career Marine who has been in more life or death battles than you've had hot meals. He's survived more infectious Flood outbreaks, greased more Covenant bad guys, and earned more medals than any other twenty soldiers. And now you get to walk a mile in his shoes!
• Dropping in as "the rookie," a new member of an elite squad of Orbital Drop Shock Troopers sent into New Mombasa on a classified recon mission, you'll be armed with specialised weaponry and upgraded technology, including silenced weapons and a VISR enhanced vision mode.
• Drop feet first into a new way to play Halo with the cooperative campaign mode, Firefight. Form a squad of your friends over System Link or Xbox LIVE and put your skills to the ultimate test against the invading Covenant war machine for glory, high scores, and achievements.
• Three all-new maps make their debut for Halo 3's traditional, chart-topping multiplayer. Heretic, Longshore, and Citadel drop in alongside the original Halo 3 Multiplayer Maps, all packed in and playable from one standalone disc.

Discover more about the build-up to the classic Halo 3

ODST stands for Orbital Drop Shock Troopers

You no longer play as the indestructible Master Chief

Sgt Johnson is available as a pre-order bonus character

You no longer play as a Spartan super soldier, but as a sort of futuristic paratrooper with less high tech armour and abilities. Much of the game is told in flashback, as you search for your missing teammates in New Mombasa and discover more of the backstory of the Halo universe.

Of course this being Halo the multiplayer is just as important as the story campaign, with the basic modes being identical to Halo 3 and using all 24 current maps. New mode Firefight though is a four player co-op mode similar to Gears of War 2's Horde - perfect for Halo fans looking for more action.

• Semi-super soldier: Get used to a dirty, more tactical style of warfare as you join the elite ODST in a story set two weeks prior to the events of Halo 3.
• Halo world: For the first time ever in a Halo game you can explore an open world environment, with the freedom to go anywhere and use any vehicle.
• Classic action: Fight in the revamped multiplayer mode from Halo 3, with access to all 24 maps released so far, including all downloadable map packs.
• War without end: New Firefight multiplayer modes introduces four play co-operative action against an unending wave of Covenant forces.