i think all they need to do is your multiplayer charactor needs different armour choices instead of just the Chief with different colors. and of course, bump up the graphics. maybe throw in firefight, maybe add the flood to it. instead of player 2 on campaign being a copy of the Chief, how about just a regular marine (but for gameplay reasons, just as strong as the Chief). add 4 player co-op campaign.
but of all of those, i would really more like better graphics, they havnt shown the flood since halo 3 and with all the graphics improoving, seeing the flood on this remake would be amazing!