Microsoft's press conference at the Electronic Entertainment Expo (E3) this year was one filled with surprises and new announcements concerning games that were already revealed. One of the biggest ones is Halo 3: ODST, which will act as a prequel to the events in Halo 3, a hugely successful title for the Xbox 360.

The new expansion will be a full game, say both its developer, Bungie, and its publisher, Microsoft, which have revealed that it will retail for 59.99 dollars when it will arrive, on September 22 this year. For those of you who want a more exclusive experience, a 99 dollar Collector's Pack will be released, featuring a special Xbox 360 wireless controller that will definitely please any Halo fan.

Halo 3: ODST will be a prequel to the original Halo 3, and will let players take the role of an ODST (Orbital Drop Shock Trooper) who must investigate the whereabouts of his scattered squad and uncover the motivations of the alien Covenant when it invaded New Mombasa. A new dimension will be added, as the main character will be able to live out the memories of his fallen brethren. 

In addition to the top-notch single-player mode, Halo 3: ODST will also introduce, besides its normal multiplayer that will feature all of the original Halo 3 maps, including the Legendary, Heroic and Mythic packs, a new mode called Firefight. Essentially, the cooperative campaign will see up to four players assume the role of a squad of ODSTs and fight together against an increasing number of enemies. Similar to the Horder mode of Gears of War 2 or the Nazi Zombie one from Call of Duty: World at War, this new campaign will certainly be appreciated by fans all around the world.

The game is now available for pre-order in both normal and collector's edition. Those who will opt to pre-order it will receive a token to unlock Sgt. Johnson as a playable character in Firefight. Don't forget that if you purchase the game, a voucher guaranteeing you access into the multiplayer beta of Halo: Reach will be included.

Is Halo 3: ODST shaping up as you wanted it to be? Leave us a comment and tell us if you plan on purchasing it.