Stunning, and not just because of the graphics
First thing you might be disappointed about though is there are not as many tracks or cars as in the previous Gran Turismo's. But that's ok, all the ones included are the one's you want, like the classic GT tracks, and cars like the Skyline, Supra, etc. Graphically, the game is amazing. The PS2 had to impress on launch and this game although it wasn't released for a few months after the PS2 was out, set the standard for graphics in driving games since. I also have Gran Turismo 4, a game released 4 years after this one, and I'd say the graphics are just the same as GT3. And that's fine because GT3's graphics are stunning and still are to this day.
The game has the same classic GT gameplay, start off with low credits, buy a used car to make some money in easy races, and work your way up to better races, with faster cars, where there's more rewards, both cash and cars is what you get for winning. Sound wise the game is excellent - the cars sound effects sound like the real thing. I think I read that since the second GT they had recorded sounds of all the cars engines noises to use in the game, and it works well. The soundtrack is ok, I only found a few songs I like, but theres alot of tracks and you can chose which ones play while your racing, so you're likely to find something you like.
To end with I'll say that this game is recommended. It's not the biggest selling game on the PS2 for nothing. I might be wrong but last time I checked it was. Cant praise it enough really, even if you have GT4, I'd say check it out anyway as it's so cheap to buy now.