If Halo 3: ODST's campaign is "Combat Distilled," then its co-op multiplayer mode, Firefight, is the product of the same process, further refined. Firefight is combat distilled, then filtered; then distilled again and again. While the story mode can already be played cooperatively with up to four players (with or without scoring enabled), Firefight re-purposes eight of the sets from the campaign missions into closed, gladiatorial arenas where the odds are heavily stacked in the Covenants' favor.
Sounds good to me.