Now that Bungie says they're done with the Halo Trilogy, what;s gonna happen now? Well They are making one last game called Halo 3 ODST

The Boxart
The game takes place after the events of Halo in New Mombasa, or the city. ODSTs are being sent in to get rid of the remaining covenant in control.

First battle of New Mombasa
So in Halo 2.25 ODST (as it should be called) is where you are the sole surviving ODST, with an amazing SMG trying to figure out what happened to everyone else in your platoon.

Your name is the Rookie, and to be more specific on who your trying to figure out their happenings, here's a list
The Captain - The Rookie's squad leader, and is a common by-the-books style officer.[15] He is voiced by famed actor, Nathan Fillion, who previously voiced Gunnery Sergeant Reynolds in Halo 3.
Mickey - One of the Rookie's squadmates, his expertise in the squad is currently unknown
Dutch - The Heavy Weapons specialist.
Romeo - The Marksman in the squad, and is quoted as being a "wiseass".
Buck - One of the Rookie's squadmates, his expertise in the squad is unknown.
And to put you back like a spartan, an AI helps you. The name of the AI is Superintendent, and he's the city's ai, and helps you along.
Now speaking f battle here's how it is. You play at night, so you must be stealthy. IF the brutes or enemies find you, they will fall back. Now this is a trap, see if you follow them, they will box you in and well...you will die fast. Just to make things different, the main villain in the game is a FEMALE, yea it is, but we don't know anything else about her. The game will also ship with new halo 3 multiplayer maps and the final vidmaster challenges.
Well that's just about it, see you guys around!