Here's a simple tweak, the ability to stand on vehicles without just falling off when they move. The return of car surfing! A certain other GTA clone (which shall not be named) made a whole mini game out of it.
Remember back in the older GTAs when you could stand/crouch in the back of a pickup and just ride around shooting people? I called it the assisted drive by. Shoot the car once and hold on!
It's kind of disappointing now that if you stand on a car and it starts to move you become drunk and just fall off.