Vehicles:I am hoping that they change the warthog a bit(IF it is going to be in the game)by adding maybe a four-wheel drive mode that allows better traction and reduced risk of rollovers at the cost of speed(just to keep the game balanced ).
I am also hoping that there will be new airborne vehicles.For instance, a fighter-jet type vehicle and a VTOL/support vehicle for both sides.
Weapons:I hope that they keep the classic human and covenant weapons still available but have additional and new weapons as well.
Customization/Personalization:I like the armory idea that halo:reach brought to us but it lacked several things I was hoping to see.The ability to customize your own helmets, chest, legs, etc. would make possibilities quite literally endless.In addition to my previous statement, The ability to choose which weapon the preview(where you can see yours and other people's spartan in the lobby)of your spartan has.Example; in halo:reach the preview always had you viewed as holding a DMR.What if I wanted my spartan to have a machine-gun turret?That would be nice. limited/legendary/pre-order edition content:I would say to have Forerunner combat skin pieces in the armory as a bonus for all editions in the "special" category.Any thing else is for 343 and gamestop to decide.
Forging:Several different forge-based maps would do nicely.One in space with space related objects, one on and under a vast sea with water-related objects, an open field, a large mountain, a tropical island, and most of all, a blank city street like area where the streets were already laid-out but fully manipulable.The ability to spawn(and drive)civilian vehicles would be outright awesome for machinima and crazy custom games.
Multiplayer:Bring back ranked and social playlists and make win/loss visible rather than kill/death.Also keep the "premium" type playlist where only people with DLC are allowed to play.Also I could care less for armor abilities and/or equipment if you can, do away with them please.
Campaign:Keep it all canon and just as epic as the previous halos.Add lots of easter eggs as we all enjoy finding those...
...and most of all make it one hell of a game!!