There are some elements in GT2 I would have liked to have seen carried over, but given the driving experience in GT3, the amazing graphics and sounds (I still contend GT1 looked better than GT2) and the fact it's properly sorted means it's no contest.
The lack of cars aside, GT3 is much better than GT2. Not just graphically, but the controls are much more fluid and realistic. That really makes the game for me.
I do miss the huge roster of cars from GT2, though....