I would make a fps/rpg/rts game
It would be based about 20 years in the future. It would be based all over the world, but the nations would no longer exist, they would all be ghost towns, with new groups building up there forces. You would go out and complete missions, against other factions, coolect resouces, recruit more people. When you were back at your factions base (which you could choose to place anywhere in the world at the beginning of the game) you would be able to buy things in an rts style screen , like base defenses, new buildings, ect, troop classes (but you would need people in your faction to have those types of classes, you could not buy troops, just change the classes). You would be able to choose where to place them as well. You could decided if you wanted to bring men with you, you could bring them all if you wanted. Or just one or two. The enemy would constantly be effecting your movements. Your base would be attacked by them, not just run and gun crazy attacks, planned out attacks. When on a mission you might run in to enemy factions depending on when you did the mission, or allies. You would be capable of launching satellites. You would be able to train recruits to be tank drivers (which you would have to find the material to build them) or pilots.
My explanation does not do my thoughts justice. This is a type of game i have always wanted.