One thing that needs to be switched up is maps in playlists. For example team slayer is missing burial mounds, terminal and relic. Think back to the original. These maps are very much missed right now on selection. And speaking of selection how about adding halo 4 into team slayer and maybe removing halo 1.
Also why not for each playlist add a social (unranked.) That way all playlists are ranked and unranked which would make it feel fresh again.