Well.. all though there is a lot to do, I think the city of Los Santos could "live-up" more, if that makes any sense..
The city is so big, but far from all the areas/places are used.
I bet we'll see at least 2 story based DLC's coming out next year. Maybe 1 focusing on the music/media/porn industry in LA and perhaps one with a heavier focus on the gangs. Perhaps you start out as a hispanic gang member breaking out from that prison. Well.. just speculations..