In my opinion I would like to see the drones come back because they were the only type of unit that didn’t need to be in a banshee and could just fly around. I would also like a new flood form and a promethean unit that could be more like the drones and can fly.
Brutes. My second favorite enemy behind the Flood.
Oh man, this is a long list.
I want to see the Banished make an entrance. Including all their vehicles, weapons, etc. I want to fight more covenant and less promethians.
The Flood. All of them, and some new ones too (perhaps infected Hunters, drones, etc)
Drones, as others mentioned. But also bring back many of the vehicles that we haven’t had for a while or that haven’t been included in a FPS game yet (thinking of Halo Wars weapons)
More than anything, bring back awesome Easter Eggs and other hidden things. Make the game fun again and the longer the campaign the happier I’d be. (So this last paragraph isn’t enemies, but I feel it’s important to a good Halo campaign)
After Halo Wars 2, Bring Back the Brutes!