State of the art for it's time.
Gran Turismo 3: A-Spec was, at the time, something much awaited and highly praised for a lot of reasons.
Some features from 2, like that of the Racing Modification option, had been removed for reasons I'm not yet aware of, but it was probably a necessary reason given the selection of cars.
It's a number of things that you take into consideration when looking at Gran Turismo 3 and why it was one of the highly heralded games.
The graphics upgrade which saw 185 new crafted cars and over 20 different tracks all receive incredible upgrades from the PS1 era's entries from Polyphony.
Sound design had also had an upgrade with cars sounding more realistic.
Not to mention it laid the ground work out for the often heavily revered Gran Turismo 4, which is still considered the best in the series today.