What i would love to see would be a campaign like reach's. I loved how you could be your own spartan in the campaign. I would also like to see characters like in ODST. you actully cared for them a little and they felt more human (cuz they were), also ODST's campaign felt a little bit more epic. But what i think is the most important thing, would be to just overhaul pretty much everything they can, armor customazation, more weapons, bigger battles, ect. They should also make it a bit more like halo 3, that would bring a LOT of people back.