upgradeable nanosuit that allows for RPG-like ability modification (in real time, and for any period of time, so dial up strength if you're out of ammo and bludgeon the enemy, or dial up speed and run away, or dial up amour and buy some extra time, etc) breather pack, gravity boots, exoskeleton, regeneration, and stealth options, etc etc;
weapon is totally modable, and has some cool new Tactical Ammo ("Tac")ammo that has a delayed effect (for optimum stealth: shoot the grunt and watch him walk into cover and fall over, hidden) and incendiary rounds, etc
enemies are North Coreans (first) and then Aliens (second).
multiple paths to solve problems
fully destructible environments (trees, vehicles that react to the placement of the shot: petrol tank, wheel, etc)