-Better Spartan Ops
-Halo 2 Length Campaign
-Arbiter Side Story Campaign, separate from the main one
-Multi-Way battle between Covenant, Prometheans, UNSC and Flood
-Driveable Elephant/Mammoth and UNSC flying vehicles
-Scarabs
-Better variety of maps - Covenant, Human and Forerunner
-Removal of custom loadouts and ordinance drops
-Less frustrating multiplayer
-Firefight
-ODSTs
-Chief's mouth shown in the epilogue
-INVASION INVASION INVASION
-Classic Infection
-Reach-tier custom options
-Insane Gametypes
-More memorable moments. Halo 4's campaign was brilliant, but none of the moments really compare to driving the tank in Metropolis or fighting two Scarabs at once.
-Mark VII armour
-Better armour customisation options
-Elites or some other race in MM
Not what I expect to see, but what I want to see.