I'm overall satisfied with Halo 4. It had a solid campaign(a bit short though, but whatever) But it's Multiplayer needs some work.
What I would do is integrate classic playlists for those who enjoy the old style.
I would also have the DMR and Plasma pistol as either a Map pickup, personal ordnance, or initial ordnance. Your class with the DMR could be kept for Spartan Ops, just not make it available for MM. The Plasma Pistol is way too useful against vehicles, I hardly get into vehicles anymore because of the Plasma Pistol and the fact that power weapons come too often in personal ordnance.
Active Camo would also be a personal ordnance power up because of Camo Snipers.
I haven't given enough thought into how I would attempt to balance AA's
There's more but I don't want a long post, just a simple idea of what I would do.