To me GTA is more about the story line then the raw destruction. Though I could see why you would like the latter.
Don't get me wrong, the storylines are usually pretty good. I'm not asking that they give crap stories. GTA III was a pretty good story, IMO. And with San Andreas, if you just give it a slight few tweaks, it could be a Four Brothers deal where she was adopting children and such. As it was, that movie really reminded me of San Andreas anyway. Did it work better with it being CJ's real mom and real siblings? Sure. But it could've worked
the other way, too.
Vice city wasn't really that customizeable. It required an Italian because the story line revolved around an ex italian mobster.
Hence why I said it needed minimal tweaking.
I'm don't think it's liberty city as it didn't even have Time square as far as I can remember.
It's Liberty City alright. They just did a better job parodying it to New York this time around. But the reason I'm so sure it's Liberty City is if you freeze frame it on one of the cars passing the pedestrians you see a police car with "LCPD" written on the side.
They also probably would've mentioned the city if it were anything new, AND to go along with the parodying New York part, they won't have two New York parodies in the GTA universe.