I don't think Cortana should come back. That was the part of Halo 4 that really stuck with me. Honestly as much as we all loved Cortana it would be painful for her to come back. Knowing she was dead, it wouldn't be the real Cortana etc.
I would like to see the Arbitar return though.
The classic Halo 3 multiplayer would be nice (it was so memorable and perfect, I didn't get the same replay out of Halo 4 multiplayer.)
Flood need to return, some how. Idk how it would play in but it would be epic
Longer campaign (I finished Halo 4 too quick)
HORNETS! need to come back
