When all the wonderful customization options for Firefight were announced in the weeks leading up to Reach’s release, the first thing that went through my mind is how awesome it was going to be playing through Campaign any way I wanted, and my disappointment when I found the custom options were for FF only really made me lose faith in Bungie’s commitment to fun.
If I can change the AI’s or my Spartan’s traits in Firefight, why can’t I do it in Campaign too? Why are my only options for Campaign four difficulty levels, two of which are too easy to be interesting and one of which doesn’t feel fair because instead of better AI the aliens just get more shields/health and damage output? And the vast majority of the skulls just introduce artificial difficulty and don’t really add anything fun.
If I want to play Pillar of Autumn with a Jetpack, no shields, 300% damage, and a bottomless Grenade Launcher, I should be able to play Pillar of Autumn with a Jetpack, no shields, 300% damage, and a bottomless Grenade Launcher.
Halo 4 should allow every custom trait available in Matchmaking or Firefight to be applied to Campaign (unless it interferes with scripted events), this will create endless replay-ability value.
You should also be able to enter a Forge-like menu and drop vehicles or weapons into your Campaign mission.
For the sake of preserving the Campaign’s story, custom Campaign options would be unlocked only after beating the game on Legendary, and maybe different options could be unlocked after achieving certain goals in Matchmaking (example: getting a Killing Spree lets you change Master Chief’s running speed and jumping height).
Edit: to prevent people from abusing this as a super easy “boosting mode”, you would not be able to earn Achievements when playing custom Campaign, nor would you earn cR if Halo 4 has it. You would not earn medals, and your stats would not be tracked.