Here's to Halo 5... Hopefully lol.
1. Bring back the Arbiter, in a cool way. After the first mission, Captain Lasky will see how much grief there is in Master Chief after the loss of Cortana. So Lasky will say "I brought you and old friend," to Master Chief's surprise, it's the Arbiter and they shake hands.
2. Would I like to see some Promethean vehicles that assemble when you sit on them.
3. Brutes are fun, bring them back. Make it so that they were chilling on high charity and now they are going into the heat of battle.
4. Bring the truce with the Elites back again, but only the Elites.
5. Bring back a veteran weapon, the plasma rifle.
6. Make a promethean turret!!!!
7.Add an armour ability that when an enemy melee's you (when you activate the armour ability) the enemy's melee damage goes straight back to them (like thorns.)
8. Let's face it, Halo 4 didn't even talk about the HALO itself. Have more storyline about the Halo rather then other planets.
9. Make Sarah Palmer horny around Chief.
10. I like spartan ops but add firefight as well (Firefight in the halo 3 odst style.)
Hope you read this 343 and apply the ideas. Good luck on Halo 5