I'd much rather a game where there were more out-of-city parts that in-city as the latter tends to get old quickly if everything looks the same.
But too much countryside and wilderness would equally be as boring because there's just not much to do in a GTA game in the asshole of nowhere.
I thought that San Andreas struck a very good balance between urban and rural areas. A few large cities with lots to do, separated by large areas of country and wilderness which was dotted with small towns.
I'd like to see the next GTA game continue on much the same theme but with a few improvements, including some of the ones you mentioned. It'd be nice to drive and explore genuinely dark areas where you need your headlights or a portable torch to explore properly. The forests in the wilderness of San Andreas were just a bit darker at night. Scare 'em up a bit by making them pitch black at night, with just the silhouettes of trees and rocks to see by unless you've got your own light and maybe just a hint of moonlight to see by if you don't have a light source of your own.
Also, as you said, some properly dense forest like in real life. Areas where you can't go by car, you have to use dirtbikes or quads to navigate along small pathways and amongst thick dense foliage.
I also like the idea of more changeable realistic weather. Sure, Los Santos wouldn't get real thick snow, just like Los Angelese doesn't (as far as I know) but it'd be nice to have a city that got snow and ice in winter and wilderness areas that also got a nice blanket of snow from time to time. Or maybe have proper hurricanes in certain areas. A city like Vice City in real life, just life Miami, should be prone to tropical storms with wild winds, heavy rains and maybe the odd bit of flooding. Shake it up a bit. These newfangled multicore processors in the new gaming consoles should be capable of handling these things.
But these are just ideas to spice up the games. Mainly I want more of the same, with maybe a bigger game world and some funky looking graphics. What I like about the GTA games on PS2 I've played is the voice-acting, the scripts, the plots, the characters, the radio stations, etc., which generally rise well above other games I've played.
Maybe some better AI in the game? How about shops and malls that only open during the day? Nightclubs that only open at night and in the early hours of the morning. Streets that are properly busy with traffic in the day and nearly empty at night. Areas with nightlife that are really busy with pedestrians and traffic during the evenings and nights but certain areas that get almost empty. Etc. etc.
And a good solid central character with a good professional voice actor. CJ was very well voiced by Young Maylay but wasn't a well balanced character. Tommy Vercetti was brilliantly voiced by Ray Liotta and was a more well balanced character, simply because they didn't try to inject any sort of poxy emotional sympathy into him whilst trying to also portray him as cold-blooded gangster. He was just a psycho gangster. Nothing more and nothing less. More of that please.
Ultimately, neither CJ or Victor Vance in Vice City Stories work to well, because we're expected to sympathise with these characters as having certain moral reasons for their behaviours (trying to restore their childhood neighbourhood, revenging their mother's death, paying for their brother's medical bills, trying to sort out their coke-addled family, etc.) while in-game they're behaving like nothing more than cold-blooded, drug-dealing, thieving thugs who have no objection whatsoever to dealing out death to anybody they feel like dealing it out to.
Don't make me try to sympathise with a drugdealing murdering gangster. Just give me a gangster and let me play him as a gangster. Just like GTAIII and Vice City did.
Okay, I'm rambling now. I'll give it a rest.
KM.