My list:
Gametypes:
-Classic (no perks, no ordinance, no loadouts, no weapon indicatiors, 4 shot BR)
-Team Snipers
-Infection (not flood)
-Team Doubles
-MLG
-Action Sack
-Assault
-One Flag CTF
-Grifball
Other:
-1-50 Skill rank system shown in game
-Better servers
-More 4v4 maps ( DLC / Community forged maps)
-DMR nerf / BR buff
These things would complete the game for me.