-In multiplayer they should have a remake from each game say Blood Gulch, District, Sandtrap, Spire and Haven.
-Drivable pelicans in multiplayer. Also maybe a few new vehicles in multiplayer say a nerfed broadsword and some forerunner vehicles like a hovercraft of somesort.
-Bring back playable elites and all the previous vehicles (falcons/hornets)
-Using playable elites create an invasion gametype or something where the humans are on a mamoth and the elites are on a scarab and you have to capture the enemy vehicle or destroy it.
-They should make the armor look decent first because the red on multiplayer is basically pink and all the armor is too similar and if it isn't it just looks stupid.
-Have a blank large room for forge where you choose the scenery e.g jungle, desert , arctic etc Then you add your own stuff to it. Say it would have 5 different settings or areas but each should be of a similar size to forge world-Plus each one would have a larger palet.Or have one massive forgeworld like a minecraft world where the surroundings change as you move over a certain distance like a real halo ring. Plus forge needs more moving pieces and more/bigger buildings. Say a long beam of light to help make real frerunner lokking stuff.
-Get rid of classes because halo 4 seems as if its trying to be COD when it isn't.
-Skulls to come back in campaign.
-More customization in armor for spartans and elites.
-bring back firefight but introduce flood and prometheans as well as covenant.
-Finally maybe have more vehicle based gametypes.