I think with GTAIV, R* did great, in terms of gameplay. the only complaints that have ever crossed my mind about the game were a few features that i think they could improve on in the next title. here are a few:
- Car Dealerships (it would be much more realistic if you were able to buy that super expensive car, like the infurnus or super GT)
- Able to have a duel pistol and SMG option. That would be pretty badass.
- More accessible buildings.
- Bicycles should come back!!
- The car body shop editing thing from GTASA, but maybe more customization.
- It Would Be Great If You Could Completely Customize Character's Appearance, but keep character details and name.
- More blood.
- More Dialog outside of missions... like, better relationship kinda stuff, more things to do with others. like in red dead redemption.
- More Guns
- More Blood
- Better radio stations
- A frying pan.