I'm playing GTA san andreas and NFS most wanted right now, and when I switch between the two games I start noticing the superiority of the graphics of NFS more and more. Even though graphics don't have to be all that important, the graphics of GTA are just a little too childish cardboard cartoony to me. The difference is just too big compared to NFS.
When you see the posibilities (like graphics NFS has), the next GTA like games will have to do far better in graphics then San Andreas. Even in GTA3 the graphics are better imo. This is not just more details its also a design issue. The ways the roads change when it rains, the way the trees looks from a distance, the way the cars break apart, birds flying, dush coming up, leaves falling from trees.
GTA san andreas doesn't give me the feeling of walking through a real city.