Halo 3: ODST is an usual outing for Bungie. An expansion pack that takes place before Halo 3, it's definitely going to offer something fresh for Halo fans.
OXM played the new Firefight mode at E3. This was the co-op mode for ODST announced during Microsoft's press conference - you're an ODST, and you and three others fight endless waves of enemies.
It's reminiscent of Gear of War 2's Horde mode, albeit not quite as frantic. Enemies arrived by drop ship (which guns the hell out of you when it comes in, so you have to hide from the turret) or seemingly from the side doors. You'll notice enemies show up without any visible drop ship around.