Although Halo 4 is pretty much complete now, what are those special little things you still want to see inside the game that haven’t been announced yet? This can be anything you want, your only limit is your imagination. 
Who’s in the cryptum, what are all the weapons, aas, and vehicles, and what are all the helmets
I’d like to see Brutes, Drones and Engineers making a comeback alongside Elites, Grunts and Jackals, together with some of the more “violent” Covenant weaponry we saw in Reach. Just because the Prometheans will be a major threat, doesn’t mean the Covenant need to be an amateur-ish, almost jokey outfit as I think they became by Halo 3. This is a force that quite easily came close to wiping out humanity, after all.
Indeed, the more I think about it, the more I’d like to see a nice, well-developed Covenant storyline throughout the trilogy. The ease with which the Covenant Empire fell apart within a matter of weeks in Halo 2/Halo 3 I found problematic from a storytelling perspective. I have a few ideas of how I’d go about doing this, which I’ll open a separate thread for later on.