I'd probably like it if they included one huge city with obvious different areas (commerical, residential, industrial, etc) one countryside an a small town or two. Make it slightly bigger than in SA, but not too stretched out. I didn't like the multiple small towns.
Btw, I think it was pretty balanced in SA, plus when not in a mission you can go into the countries and pick on cops and go off-road car chasing - usually with hilarious results. But the area restriction has got to go, it's kinda odd that they set up total road blocks just so CJ can't pass.