Weapons and equipment
add a new grenade ‘homies’ - which would home-on an opponent but would explode when its x-meters away from it. Should not kill a full health spartan but should do damage equivalent of 2 DMR bullets !!!
return equipment
return DMR/BR (i like both :)). I like the new range of DMR - so if BR is returning then add some range to it.
return SMG.
return shorter range shotgun.
return mauler.
return Sniper like reach but smaller hitscan or bullet-magnetism.
Return Grenade Lawnchair - one of the best weapon in reach
fix plasma lawunchair - it is overpowered
return focus rifle with a little boost to it
return missile pod
Add weapon tweaking - like clipsize, rate of fire etc - would allow creating awesome new gametypes
In AA pickup gametypes allow the AA of a dead person to be picked up immediately - like grenates and weapons
nerf grenades a teeny-weeny bit - now that in TU the default speed has been tweaked - it means that grenades have already been tweaked a bit.
add new weapon - needle blaster - would be covie equivalent of shotgun.
Movement and Speed
Make sure default jump height makes us feel like a spartan
Health
Health pack vs Health regen
Add option to tweak sheilds to invincible - so that only headshots are registered. (This might already be in :P)
Vehicles
Tweak - Vehicle health more like H3 than H:R -
tweak - Banshee is too overpowered - balance it
return rocket on warthog (forgive my ignorance i forgot the actual name of the vehicle) - love that vehicle
Playlists
1-50 ranking Definitely 
- i loved playing for a skill based rank rather than to gather cr. Arena sucks :(.
Ranks / skill should be win based rather than individual score based. Ppl in H3 used to debate that rank should be individual based (i was not one of them)- and now hope they would have learnt their lesson and would like to come back to win based ranking.
Try and find a fix for boosters !!!
Gametypes
return headhunter
return stockpile
return VIP
return rocket hog race.
add if possible - i personally cant think of any new gametype
return Spantan vs Elite gametypes
AAs
Like most of the things AAs can be fixed/tweaked - now that their unbalance nature is known they too like weapons can be balanced. But i think that AA might not return as someone from 343 said that in H4 trailer MasterChief is not wearing a jetpack but a space-propellor or something. (dont have link to prove that 
). I would definitely like them too come back - at least if I wanted I should be able to play them in “Customs”
Allow AA tweaking - i know it would be extremely tough but worth a shot. Things like its duration/rate at which AA burns. For each AA capability to tweak it like removing radar jammers for Camo.
Armor
Add more for other players - personally not really intersted in dressing up my spartan but is fun before match starts :).
Halo Stats
return Shots fired vs shots missed for every weapon
return average kill and death distance for every weapon
make APIs free - so that apps can be developed faster. obviously the apps created would not be saleable but would be free.
Maps
remove swordbase
return narrows - loved that map
Graphics
Improve it as much as possible but focus should remain more on gameplay. Halo is not BF3/COD.
Add visual cues to recognise the AA of a player by looking at him - the cue should be visible from front and back.
Forge and spawns
Add some color to it.
Allow spawning of weapons if they have been dropped at fixed time. Or if they are dropped after their spawn time then they should be spawned immediately.
return bro-spawns
add an option to choose your spawn point (ofcourse the choice will be restricted to one of your teams spawn points )
Theater
Add multiple simultaneous views.
If possible add more accuracy to opponent screens.
Firefight
Add firefight against spartans - this would allow us to actually practice our shooting on real opponents.
Commendations
Add more if possible - I know removing AAs would reduce a lot of commendations.