How about a prequel?
You are the Rookie, and its time to explore a bit of his past in the battles he kicked ass in before he joined Buck, Romeo, Dare, Mickey and Dutch.
I also like the idea of having a Section 8: Prejudice style respawn in firefight and multiplayer, where you select you're dropping point and drop feet first into hell.
I also would love to see customizable ODST armor pieces and the helmet on/off option, as well as sprint, and different vision modes through the VISR. I'd also like a good mix of light maps, such as Reach's Forge World, but also some more somber maps like the Ruins of New Alexandria. Maybe like a ruined version of Reach's Reflection, but just all shot up and dark.
Also, I'd like to see Brute Slayer. How funny would that be?
As well as ODST vs. Brutes invasion. No elites, because that would ruin the old familiar Halo 3 feeling.
My perspective on a second ODST game would be this, all summed up: A game with new features and graphics, much like Reach's, but with that old familiar Halo 3 feeling. Also, add ODST forge, and multiplayer in addition to a new campaign. Make the firefight have its own forge version and also let the player change different settings in firefight, excluding the ability to make yourself invincible, lol.
All you guys ideas are amazing, i'd like to see a Halo 4: ODST 2 come out someday, with many of these awesome features.