Take a lesson on GTA IVs euphoria physic. GTA V was a backstep in this regard. Super realistic physics can make for some hilarity. I never realized how import they were until this recent COD alpha came out. Those animations were so detailed and it made it feel so much more immersive.
I feel like GTA needs make this sort of progression in many ways. Hand never felt powerful and I hated their sounds. They need to feel heavy like in Max Payne 3. That was their peak of gameplay in my opinion.
Also, don't focus so much on how much terrain there is. Use what you learned from red dead and expand. For example, GTA V was huge but there was a lot of nothingness. Have more buildings in GTA V which have levels and people working, going to their apartments, parties. Make the city feel loved in.
I know some people may hate me saying this, but light rpg elements could do this game some good. Be able to talk to all NPCs, but expand further. I want to be able to mug people and Rob houses, get into fights, hit on women ( not PC but shut up).