These are the features I really want in GTA V:
- Buyable houses and apartments
- Buyable businesses
- Enterable police stations
- A wide selection of weapons
- Weapon Customization
- Vehicle Customization
- Gang territories
- Area 69
- Multiple cities
- Multiple airports
- Job system: taxi, ambulance, garbage man, street sweeper, postal worker, trucker
- Enterable stores where non-weapon items can be purchased
- Operational car dealers
- Spike strips
- Drivable trains/subways
- Drug system
- Trunk system
- Dedicated servers
- Robbable houses/apartments, stores, and banks
- Disguise system: wearing certain clothing allows at least temporary acceptance by a faction
- Police dogs
- The ability to decapitate and blow off limbs
- Sewer system
- Passport system
- Functional airports (planes can be flown as a passenger, but at a cost)
- Usable gyms
- Functioning movie theaters (similar to the comedy clubs in GTA IV)
- Recurring hitman side missions
- Functioning and usable casinos
I'll add more to the list as I think of them.