Probably all ready covered but
The DO's
DO - bring back the buildable shield
DO - bring back the maxis drone or similar
DO - bring back wunderfizz
DO - bring back in game challenges (soul chest for example but different challenges throughout the game, one to be done by round 10, one to be done between round 10 / 20 etc - if going for a high round, then they can be disabled on solo if need be)
DO - bring back dig spots or similar
DO - bring back traps
DO - bring back easter eggs, only make them worthwhile - you know it makes sense - the black ops 2 easter eggs are nonsensical & a waste of time, make them harder to achieve and make them longer with bigger rewards.
DO - bring back WaW, Black Ops, Black Ops 2 maps, completely reworked for the next gen systems and done the way they where intended. You know you can bring them back, even if it's a super pack with a nod to the community - you know it makes sense.
DO - bring back ranks, I don't see a problem with them, but punish people who quit games, de-rank them immediately and tell them why they have been deranked in game. If they dashboard, next time the launch the game and enter zombies - put a big flashing notice up saying, "you have been deranked for dashboarding or just backing out of a game because yer a twat and sin binned for 1 hour". (increasing in time after each infringment)
The Don'ts
DON'T - bring back the match making system you have had on black ops, it's shit (no other word to use for it, so excuse the profanity)
DON'T - bring back buildables such as the trample steam
DON'T - bring back reasons for players to quit lobby's or games. If we want to play with mic's let us select lobby's with mic'd players - if we don't let us select no mic'd lobbys. Let us select whether we want a 2, 3, 4 player lobby.