If infinite’s story mode is going to be good. It needs a new enemy type. We can’t just have the same old covenant. Introduce a new species or revamp old enemies. Maybe the hunters can drop the armor and will use the worms-like body to become more agile and dodge enemy fire. Maybe there’s an enemy type that burrows underground or something. maybe Prometheans can remotely control electronics and try to splatter you with a ghost or something. But we need something new
"New" is what people didn't like about Halo 4 and Halo 5: Guardians. If it ain't broke, don't fix it.
Every Halo has had new enemies in it.

Halo 2 added, for example, brutes & drones.

Halo 3 added flood pure variants.

Halo 3: ODST added engineers.

Halo Reach added skirmishers

And so on, these are pretty bare-bones examples given variation has been added through introducing new enemy vehicles & weapons too, the list goes on.

As so, I don't expect anything too drastic in form of new additions but Id say it's pretty certain there will be at least something new in form of enemy variation, I doubt this will be the first large scale Halo to break that tradition.

Though I do hope similar disappearance for promethean faction as what happened earlier to the flood & sentinel factions, though sentinels disappearance hasn't been handled that well, they pretty much were just replaced with another robotic faction.
I'm desperately hoping for a revamp of the Prometheans, they need it.
I think a new enemy type should be for each faction.

Humans- Insurrectionist, especially since we have fought against Human AI in Warzone and boy do their ARs hurt. They can have health a little bit above grunts or jackals if you're not headshotting them. Maybe have them use cover?

Covenant- Maybe bring back the brutes, they have a lot of Variation in Halo Wars 2. Especially the Voridus' Brutes with the Infusion, or Brute Riders, even somehow getting an Atriox's Chosen back would be interesting. Maybe a Goliath those look horrifying or a Hunter Captain?

Forerunner- Since the Forerunner keep evolving, I'd say a new type of sentinel like a Retriever (Yes I know they are huge in the book) as a boss fight, or a Sentinel from Operation: Spearbreaker. Or maybe a Sentinel that can combine with other sentinels that can be stronger. Even the Promethean Knights can do another upgrade and be bosses on their own now.

Flood: There are so many things you can do with new Flood variants I'd be surprised at what 343i can cook up with.

Created: Maybe have them use machines to attack you and use Plasma weaponry to disable or overload their chips?
I wouldn't be adding new enemies rather revamping old ones more specifically the promethans they DESPERATELY need a revamp if 343 is having them as half of the gameplay, they need

1. Something to differentiate each promitian unit, a knight with a scattershot looks almost the same as a knight with a lightrifle, maybe use different colors?

2 Find some other way to spawn them in it just baffles me how the devs thought it would be okay to just make the promotians just show up like spawning a prop in forge, give them droppods or a transport

3 make there guns not all either homing weapons or hitscan, make some of them unguided projectials so we can dodge them and not have hide in cover every time

i could go more but you get the point prometians need some BIG improvements and new enemies are not a priority IMO
I think they should mostly add new enemies by creating new enemy classes within factions. I don't want to see a radically new faction just yet. Occasionally fighting hostile animals/wildlife might be fun, but 343 shouldn't go too far with it.
x N7 117 x wrote:
"New" is what people didn't like about Halo 4 and Halo 5: Guardians. If it ain't broke, don't fix it.
"Same," is what people didn't like about Modern Warfare 3.
If they are in the game at all, I hope the Prometheans are fundamentally redesigned to the point that they're effectively "new" enemy types. They simply aren't enjoyable to fight in their current iteration and you feel like you're shooting a metal brick.

Additionally, I believe there is so much room for improvement on some existing factions. Hunters could have various "stages" to them like, for example, they have damageable armor pieces which, once destroyed, allow for one-shot kills.