This is a list of things I would like to see in Halo 4 that were in Halo Reach:
Headhunter
Invasion
Active Roster
Generator Defense
Falcons
Flyable Pelicans
Buildings which crumble before your eyes
Space Combat
Some first-person cutscenes
Zero gravity in multiplayer maps
Skirmishers
Heavy rainfall
Basically everything stated in the OP I would like to see return. here a few of my suggestions.
Un-Hunched Elites
Plasma Rifle and Plasma Pistol being usable
Driveable Phantoms
Shades in Forge
All weapons being place able in every map in Forge
Plasma Repeater
Needle Rifle