STORY IDEAS
1st: Halo 5 story line should foucus on the covenent,promethians,the arbiter and maybe on how cortana can be brought back. Try to balance the story out.
2nd: The arbiter should make an entrance in halo 5 in the beginning. For example the arbiter makes it right out side the borders of the earths orbital defense grid system and sends a message that they are not their enemies. The chief here's the news about him and asks to send him in to get some explanations about what has happen with his covenant. So he explains and they once again become allies and fight on to exterminate the heretic covenant once in for all. The covenet should be able to speak English if not then at least the arbiters covenet should be able to.
3rd: The Promethians should obviously play a big role in halo 5. As in find out more about them and their structures and weapons.
4th: If halo 5 story involves trying to bring cortana back its should not be entirely focus on that single objective.
5th: The old halo music should make a return along with some new music.
GUNS/VEHICLE
1st: some guns from the previous halos should be brought back and try to bring dul-weilding back. An air vehicle should be introduced for the humans and possible forruner vehicles.
2nd: New guns should be brought in.
MULTIPLAYER IDEAS
1st: Elites should be playable in the multiplayer.
2nd: A true ranking system should be introduce.
3rd: Better looking armor.
4th: Old and new gametypes.
5th: No load outs ( I didn't really like that)
FORGE IDEAS
1st: Better forging maps and environments.
2nd: Option to change weather.
3rd: Entirely new forge pieces
4th: Better affects like fog,dust storm and blizzards.
Also don't make the elites look like the ones from reach in any way make them look more like halo 3.
And involve the flood and maybe even the brutes