UNSC flying vehicles returning, hornet or falcon, perhaps something new.
Character interactions between Blue Team to feel like they gel well.
No QTE for a boss fight or endgame. Have a vehicle run, boss fight, or anything else.
Missions to have more epicness and scale design wise. Look for Halo 3 and some Halo 2 missions for examples. Like The Covenant, The Ark, Metropolis etc. The only reason I say this is because Halo 4 felt WAY too closed in most of the time. Probably because of Hardware limitations but still.
More Campaign missions in general, 8 is not enough really. And if Flood do return, either have a level to set them up or a level about them. EX. 343 Guilty Spark from Halo CE or Floodgate from Halo 3, NOT shaped after CORTANA.
The Precursors to actually have more of a role in the games. They are a bigger part of the Universe than people think, and the Flood can have a new side to study with the Precursor's presence.
A multiplayer with more longevity. Hopefully the SR ranking up is longer than Halo 4's. The True skill should help this.
Have Arbiter be more like Halo 2 Arbiter and not the Halo 3 version character wise... and plz don't kill him.
Bring them Scarabs back bahby.
More variety in Armor and Armor combinations. Less helmet More visor.
Bring back Multi-team. That's a just for me, personally. I miss it alot, and Halo hasn't seen it in a while.
343 to continue what they're doing with the Lore, which has so far been excellent.
That one mission where everything fights each other and you get to sit back and watch, alla High Charity for an example.
That's all I have for now. There's more, just can't think of it.