1. A little bit graphics and gameplay improvements.
2. A city which is not surrounded by vast waters.(duh, it's really weird to see a city enclosed in the ocean)
3. General realistic game. That means, if possible, try to make the whole GTA much more realistic. Like peds that do what everyday people do, buildings where you can enter, and when you take injuries, the protagonist must have the real gestures that an injured person does.
4. Beautiful spots like waterfalls, large lake, large mall, etc.
5. All new gangs or a GTA which features many gang wars.