I want more character customisation than GTA SA and most definitely IV...the customisation in that was terrible.
I want a wider range of radio genre's...In SA I loved Radio X as they had songs such as Faith No More - Midlife Crysis, Ozzy - Hellraiser, Rage Against The Machine - Killing In The Name, Depeche Mode - Personal Jesus, Danzig - Mother, Guns 'n' Roses - Welcome to the Jungle, Soundgarded - Rusty Cage, Jane's Addiction - Been Caught Stealing and then there was K-Rose with Conway Twitty and Loretta Lynn - Louisiana Woman, Mississippi Man. (All brilliant tracks with some of my favourite bands)
GTA IV only had Burro Banton - Badder Den Dem, Bunji Garlin - Brrrt, Chuck Fenda - All About Da Weed, Buju Banton - Driver on Massive B (all of which were semi-decent), Jean Michel Jarre - Oxygène Pt 4, Philip Glass - Pruit Igoe on The Journey (Awesome tracks, best in the game IMHO), and I think Liberty Rock had some alright tunes too but other than that, I thought the tracks didn't meet my expectations really.
If multiplayer is to be included (which it undoubtedly will), at least give it a point...a section specifically for free-for-all free roam is necessary as GTA IVs annoyed the faeces out of me.
I want to be able to hunt and gain something from doing so as was done in RDR
More non-major character interactions.
Drivable trains that can derail.
A usable bus service (although I have heard this will be included with a city tour too)
Some dual-wielding (possibly with different weapons (e.g. pistol and SMG).
Gun customisation perhaps.
Property customisation (E.g. furniture, decorations, perhaps wallpaper)
More personalisation abilities from the iFruit.
Personalised radio station (with tracks that are on your console/pc. I am aware that PC had that ability and perhaps 360 but PS3 didn't.)
A prone stance.
Drive-by's 'cause "Suckers are hiddin' Jump behind the bush when they see me driving by, Hangin' out my window, And my magnum takin' out some puto's " (Cypress Hill/Rage Against The Machine - How I could just kill a man).
Burglary of homes.
Visible unequipped weapons or maybe in a rucksack rather than him pulling them from thin air.
I'm sure there is more i could think of but for now that is my contribution. ROLL ON SEPTEMBER!