For me, I’d like most of them to return, including the Beta playlist like in Reach so we can test the new ideas they want to add. I mainly want to see an Arena style playlist again. I quite enjoy going on the arena and trying to get into a high tier. I quite like to play like that.
I think you should only be able to enter the arena after the first few ranks, such as rank 10. You should also be placed with people of similar skill levels when awaiting to be put in a tier, even in the first leg of it. Finally, when you have a tier it should be next to your rank, always. Even if your not playing in the arena playlist, it would be nice for people to see what tier you managed to get to.
Granted, it does need some improving, but I’d like to see where the arena could go. I also think there should be an arena for the “classic” Halo playlist and Halo 4 style arena so you can choose which you would rather play in.