One can only share revering feedback about GT3. I think of it as a royalty among the family of games. GT3 alone has sold countless PS2s, while setting the de-facto standard for the ultimate and utterly-professional driving sim. The scope of campaign modes, car-enhancements, race tracks, league settings, etc is mind-boggling. You can easily spend 50-60 hours playing GT3 without being bored in the least. This plethora of modes and design sophistication gives GT3 the ultimate gaming jewels – awesome repeat value, outstanding gameplay depth, and loyal gamers' following.
The dual player mode is just as impressive as the single player mode, but like in most driving sims the dual player mode is merely a function of the single player. GT3 becomes exponentially more fun to play with a buddy after you have unlocked the majority of it in single player settings. One ding on the multiplayer function is that it has two people max.
The driving physics are outstanding; the sounds are just as good. The graphics are good also but after the arrival of games like Gotham and GT 2002 I think there's room for much improvement the GT franchise can achieve in its fourth installment.
If you own the PS2, buying GT3 is a no brainer – with the Greatest Hits price tag, GT3 is one of the best gaming investments you will make.