I just had a thought about Halo: Reach. While Bungie may be putting the Halo 3 engine to rest, there's nothing stopping them from using a storytelling structure like ODST's flashbacks for the single player campaign. That was really a great move for that game, and for a story that covers the destruction of the human race's second-most well-defended planet, it could work even better. Play as a weak little marine on the surface, getting wupped by Wraiths, then play as a MAC gun operator, shooting down approaching Covenent ships (just kidding. Bungie never did those forced turret-section shooting galleries so many other FPSs insist on pushing on us )

But there is something we can be sure about: The Elites will be our enemies again. So those who hated the brutes can now rejoice. (what was wrong with the brutes? I mean, I liked fighting the Elites, but the brutes were perfectly adequate replacements I think)