I guess I'm the only person that would be perfectly happy with a new story.
If Rockstar changed nothing but the story and city then I'd be fine with San Andreas. They have a physics engine that allows for decent shooting, perfect car controls, and perfect crash realism. The graphics are decent, but I agree that it's about time for a overhaul. Not sure what else the PS2 can do with a GTA-type engine, though...the city is too big to make it that complicated. Rockstar has already coded the game so that nothing exists until you're about 100 feet from it (the city renders itself as you get near each location...each car, pedestrian, etc. doesn't even exist unless you drive near it) to boost performance, so there's not much else to do. The voice acting is top-notch, the music rocks, and the stories are already incredible. I know I'm repeating myself, but I only want Rockstar to change the city and story. Anything after that is just bonus material to an already near-perfect series.
-Lasereth