I think Reach and ODST mixed would be a perfect Firefight. ODST had the original survival challenge down yet I like Halo Reaches A.I and customability. I say the maps don’t mean much because Halo 4 will have new maps.
First Off
Use old and new enemies. Even if they are not enemies in Halo 4. This includes the Covenant, Flood, Sentinels and whatever else is new.
Use more vehicles. We need more warthogs, covenant vehicles and even tanks. As well as turrets. It would be a blast. They could work as unlockables or original get and use.
I don’t assume Halo 4 will use health packs. Instead A.I should be top notch and more aggressive. Players would need to use teamwork more often to “camp and regen”. Because alone it would be very hard.
Limit ammo. Halo Reach messed up that but giving you infinite ammo. Maybe a bonus or an option but it should be like ODST. Limit it. Make you scrap for ammo.
Limit lives more often. On normal Halo 4 firefight we should go back to 7 lives shared between 2-4 players. Each round however should give 1 life to each player that lives.
A.I needs to be aggressive. On Reach if you put “eagle eye and sharp” it makes a near perfect A.I. They act like they should.
Bonus. Bosses. Objectives. Allies
Allies should exist in a few maps. Like the new map however not just ODST. Some Marines as well. Or others such as sentinels and maybe Elites.
Objectives. Not just defending generators. Have missions such as planting a bomb into some base(s). Defend a territory(s). Kill some enemy leader(s). And other things. Almost like mini campaign missions. But with Firefight laws. Could work WONDERS in Firefight verses.
Bosses. Lets bring in bosses. Which could be after Bonus Rounds. Bosses could include
1-A scarab or two: Scarabs would act the same way they did in Halo 3. However much stronger. Scarabs will have a few troops on them but scarabs don’t come with group forces.
2-Phantom/Spirit attack: Phantoms and Spirits come and attack, they don’t drop off troops but will shoot and bomb you.
3-Drop Pods: A large group of elites drop down, high class Elites and stealth ones. All with swords, leaders get rifles.
4-Wraith attack: Several Wraiths and troops land across the map and will bomb the player(s). They will be deadly accurate, Be careful!
5-Flood infection: The map gets flood foggy and an array of flood will attack the player
Forge
Forge should exist to some degree in Firefight. Not as advanced as normal forge 3.0 [for balance reasons]. Forge in FF you could
1-Make simple bases/barriers/forts [pre-set structures to prevent unfair blockage and such]
2-Place spawn zones and loadout cams
3-Place weapon crates
4-Where drop ships will drop off troops [enemy and ally]
5-Vehicle and turret placement
6-Objective areas