more after the jump

-Halo 3 ODST Campaign, which puts the player in control of different characters in New Mombasa during the events leading up to Halo 3.
-Halo 3 ODST “Firefight” mode, “a new cooperative multiplayer* mode where up to four players can assume the role of an ODST squad and fight together to take on increasingly challenging waves of enemies.” Also: “As an ODST squad, you will face increasingly challenging waves of enemies together, striving to earn the highest scores possible, while various “Halo 3″ “Skulls” are progressively activated.” (It sounds to us like Gears of War 2′s Horde mode.)
-Three new Halo 3 multiplayer maps on a standalone disc
-The more than 20 downloadable maps previously released for Halo 3 in the Legendary, Heroic and Mythic map packs.
-A key to the forthcoming multiplayer beta for the fall 2010 Bungie game Halo: Reach