About this topic,
From IV to V I'd like to see:
A better selection of guns/weaponry. IV was really lacking on the type of weapon as well as the ammunition limit (unless I was high and there was no limit...)
Ammunations should make a return, trademark part of GTA's that I missed in IV
Better environment sounds. Playing GTA 3 recently I was wondering why I liked the atmosphere so much of that game and I think it was because of the sound effects (Head radio station had music playing when you went by it, the Sawmill in Portland would sound like a mill if close enough, music at salvatore's mansion, hear the wind roll in, etc.)
Pedestrains didn't have quite the standard of one liners that IV had. That sucked too and hope we get maybe fewer lines but more rememberable ones (My mother's my sister!, come on you all remember that one.)
Lead character that complained about killing people/getting his hands dirty again for money. Couldn't go on rampages with him because of that.
I actually missed the onslaught of police cars that would happen when you would get a 3 or higher warrant level. It always seemed like in IV you had to do a lot of work to rack up a 2 or higher wanted level. Get rid of the grid system and put more police bribes in to drive through when running from the cops.
I'm hoping for less radio stations but with more fitting songs to GTA. Granted VC and SA were in the past and you could easily pick better songs in an era that's already past but GTA III was new at the time and had a lot of unkowns/non-mainstream artists that were great. IV had several radio stations that I never listened to and Integrity 2.0 I think was the weakest talk radio show in GTA history.
Driving physics! Sometimes the driving physics in GTA IV were unfun and didn't have the same "get in and floor it" feel as previous installments in the franchise. I'm not saying lets go back the the SA physics were you crashed freeways by slowing down but some less realism would be appreciated.
Walking physics, Niko seemed to handle really poorly or when I would run into someone I could only stagger backwards until I fell over sometimes. I didn't need to push everyone out of the way when I am running in the subway, slowed me down too much for my liking.
I haven't played RDR or the episodes of Liberty City so I don't know if Rockstar has become more realistic or less or if they have become fun again.