-A larger weapon variety
-A duck~n~cover/shield option
-Fully constomizable weapons
-The ability to call in for help when available
A better enemy layout:
-Tactical co-op among enemy comabatants
-The ability to call for backup when available
-Better AI
-Dialog between members of opposing faction
Repair/Builing:
-Ability to repair rusted up vehicles for personal use
-Custom building/creation
-The ability to sell schematic you've come up with
Vehicles:
-Vertibirds
-Hover cars
-Bikes
-Tanks
-Tamed/wrangled creatures
I'm sure I'll think of more later.