In Halo 4 I feel it needs:
A Vehicle based Mission. So mainly Warthog driving, kind of like Halo
A Tank based Mission, so the Ark for instance.
A Tutorial Mission
A Cinematic Mission
A Stealth Mission. Not with a sniper but trying to avoid forces attacking you and if you are found you have to revert to last checkpoint
A Sniper Mission. Perhaps backing up forces while they attack
A Flood Mission. Essentially just filled up to the brim with Flood. Like the Library or Cortana.
A Piloting Mission
and lastly what I feel has been lacking from the Halo series mission wise is a full scale war kind of mission, so with lots of AI
All of these kinds of missions obviously don’t run the whole way through with a tank or going all the way through piloting a vehicle, but these take up a lot of the mission. Well apart from the Flood Mission as they should be the only enemies in that mission.