In lieu of a complete multiplayer option, ODST includes Halo 3's multiplayer game modes contained on a separate disc. The offering contains 21 multiplayer maps released for Halo 3 as well as 3 additional maps titled Citadel, Heretic, and Longshore. The maps are tied into Halo 3's achievements. Along with the Halo 3 maps, ODST includes a version of the Forge map editor[—a utility that allows player customizations of multiplayer levels.
ODST contains a cooperative game mode called Firefight, where players take on increasingly difficult waves of enemies in a timed survival game. Firefight can be played cooperatively with up to three other players via networked consoles (System Link) or Microsoft multiplayer service Xbox Live or with up to 2 players on the same console in splitscreen mode. Players start Firefight with only the Rookie as a playable character; completing the campaign mode unlocks other characters and maps. Players are awarded medals for making special kills, and individual and team scores are tracked throughout the games. Inside Firefight, players have a shared pool of seven lives, which are replenished after completing five rounds. Adding to the difficulty are modifiers called "skulls", which give enemies new abilities or a handicap to the player – the "Catch" skull, for example, causes enemies to throw greater numbers of grenades. Each of the first three rounds in a set activates a different skull. On the fourth set, all skulls are activated and the players must survive 60 seconds
So I'm just starting to play this online and it's turning out to be really fun. So far I've played Crazy King and Oddball. It's proving to be quite fun and challenging trying to get the control points for Crazy King, and a major pain in the butt to get the skull.
If anyone wants to join in, add my gamertag NekoArcNet