Haven't got IV so not too sure but in the next GTA i'm so keen on NOT using America. I'm more interested in them trying Europe or any other country. Possible female protagonist cause that'd be so cool haha. Um... Instead of unlocking a bridge to the next island i think it should be letting you move to another country then another instead of having 3 islands in one city. Improved weapons. As much stealth as possible.
I also think skateboards would be cool or something, like what they did in Bully, press a button and you're riding a board, cause walking is boring and jacking cars etc takes too long and you need one near you in the first place.
Definitely car customisation.
Like San Andreas with the wide variety of terrain and places to go and how they had the woods and desert etc i love that kind of thing. Not like Liberty city with just buildings.
Can't think of anything else at the moment