In my personal opinion I would like to add to Halo 5 what was taken out in Halo 4 and Halo Reach:
-I think dual wielding is a must have but it isn't all to overpowered because it takes the grenade and melee ability
-The Falcon and the hornet should be added seeing that there is only one flying vehicle available. There also should be a brand new Covenant air vehicle and a Forerunner one as well add the revelent and some brute vehicles
-Bring back the ability to be an elite
-firefight 2.0 add more options and wave system add in all 3 flood promethians and elites and do things such as like unlock buildings in game to expand and earn special guns and vehicles to survive
-add more guns many were taken out and pretty much people used 3 of the primaries the dmr br and assault rifle
-bring back the elephant into multiplayer and other things to the maps that can be used in the background
- add more recreated map and newly idead map so Exile a Ragnarock arent used every time and add life to the maps so they aren't dead and expand the maps
- add the racing mode back in forge and more add ins
-make the armor more distinct because other than the head everything was identical
-add more weekly challenges and a way of keeping the player addicted to matchmaking such as exclusives for higher level and groups that take over after level 50
-longer campaign and add where master chief visits a uninhabited planet but brute remains are left and you could use all they had like vehicles and weapons