1. The Spirit of Fire, It would awesome to for the return of the ship. Have the ship be found a drift in space by a UNSC and with Serina, the ship "smart" AI, in a massive state of rampancy. Now have the crew still in cryo and the UNSC unload the old UNSC vehicles such as the Grizzly, Hawk, vulture ect and have such vehicle upgraded to be used in the campaign/multiplayer.
2. Forge, The forge was a let down the new thing like you added were cool, but the map seemed small. Few things need added Large maps AKA forge world, a Blank map as in sand box, we need a map with nothing on it sand box is a good example, a large map with so many places to build. The elephant/mammoth in forge map these vehicles will be nice to add also if add make be able to be destroyed. bring back classic forge maps, as well as UNLIMITED use of a single item.
3. Custom games, Halo 4 custom game was a major let down you remove the ability to make random weapon loadouts, the new infection it really ruins the way to make creative game modes, it was a down grade to reach you down graded the ability to make creative games. So this is whats needed from halo 3 regenerate granades, halo 3 inderstuctible vehicles, add back halo 3/ halo reach infection.
4. theater, only two things to say have halo 3 theatermode which your able to have groups of people watch a clip together, as well able to record capaign.
5. I want to fing the skull dont give them to us we want to find them for crying out loud,
over all 343 step it up go back to other halo games and see what made them so great.