1. Having not all havoc in Paragon City being caused by supervillains, but sometimes by natural disasters like tornadoes, hurricanes, earthquakes, etc.
2. Expanding the scope of the environment so that not just Paragon City is the only place that we must protect; but other countries, the planet Earth or even the universe/multiverse.
3. Having the entire environment be interactive like lifting a car or a slab of concrete to rescue a civilian trapped underneath it and/or to throw it at an enemy. And villains could work to attempt to destroy the environment themselves.
....Damn! I suddenly want to play this game now!