This is my opinion on what Black Ops 3 needs. (Whatever Black Ops they will call it)
Maps:
Treyarch does the best creating maps IMO. Keep the 3-lane maps that you guys always make they're better than the ones with a bunch of crap everywhere. Keep the smaller maps. IW really messed up with maps like Stonehaven and Siege, make more maps the size of Raid, Standoff, Studio, etc.
Create a Class:
Keep the pick 10 system or make it even better. That is hands down the best CaC system.
League Play:
League Play was great. Bring it back.
Killstreaks/Scorestreaks:
BRING BACK SCORESTREAKS! Please add a MOAB or KEM type of killstreak. That bummed people not having one in BO2. Maybe add a type of specialist package. Bring back the RC/XD and the paths for it you had in the original Black Ops.
Game Modes:
Keep 2 round domination. Bring back Hardpoint. Add more party modes. You guys need more modes like Infected and those type.
Customization:
The colors for Treyarch games are always better than IW so keep them. More camos, more vibrant or animated like Cyborg. Gold and Diamond or other gems. Reticles and their colors, lens colors, maybe even iron sites colors. Colored clan tag options. Maybe even camos for equipment, grenades, tomahawks, claymores, etc. Soldier customization.
Zombies:
Keep up the good work.
Try and make it the best connection yet. Destructible environments. Dolphin diving.