Halo ODST marks the end of the Halo trilogy

Bungie doesn't intend to go back to the Halo trilogy following the release of ODST.

Bungie's community manager Brian Jarrad has told VG247 that Halo: Reach is very much distinct from the previous three Halo games - a stand-alone prequel, with ODST being the last entrance in that trilogy's universe:

"For now Reach is definitely our next big thing, and it doesn't really fit into the Halo trilogy itself. It's definitely a prequel, standalone offering, so we don't have current plans to go back and inject more content into the current Halo trilogy.

"I think ODST is going to be a nice exclamation point, a nice rounding up of multiplayer content and a different side-story, but right now Reach is our focus."

Halo ODST will bring the fight back to earth this September.