My idea: SMG power drops after certain distance (on all weapons, maybe?), making it mid-range weapon, and having a good reason for AR (Assault Rifle). Gravity affected bullets would make a nice place for the sniper rifle. And vehicles for heavier weapons (RPGs, mountable machine guns, mortars, etc). Melee attack for weapons. Anything else? Oh yeah, Pick-shovel! A combination of a pick and a shovel! (example: http://www.amazon.com/Coleman-Folding-Shovel-and-Pick/dp/B0009PUTES )