You should be able to take an elevator or something down to the city and explore different sectors in the cities. Then there should be events when small fallen enemies get in and you have to protect the people living in the city. And do quests for other civilians to help them. Like buying some items or a specific gun for a store or something. And you should be able to buy I house for sale in the city and upgrade that house with wardrobe and cool decor and furniture. And just like a huge open world where you can interact with people. And...and... An arena in the middle of the city where once you go into it you can fight other CPUs or other players for fun or you can just watch from the stands. And there should be a feature to make you not hold any weapons (kinda like the no weapon glitch) where you can walk in the city without holding a gun. I have tons of other ideas but I just wanted to share this one.