Very simple, addictive and at the same time could be very irritating.
In 2009 it looks good. Cars are very detailed, colourful (check free walk mode in garage and you will understand what I'm talking about). Trees look not very good in the game. Even in Gran Turismo 3 and 4 trees look much better in my opinion. Tracks are very good designed, but they don't surprise: simple, practical - just for racing. Night driving in Tokyo, LV looks fabulous.
SFX, soundtrack:
SFX is great, but sometimes it lacks more detailed sounds.
I don't remember soundtrack, but there was an electro music. Switched it off after some time. Just couldn't concentrate for racing.
Game-play:
Very simple. There are many racing modes like hot lap, street race, cone driving, eliminator etc. Championships contain numerous races. For wining a race you get a medal (bronze, silver, gold, platinum). In the beginning it could be very trivial and simple (read - boring), but with a progress game-play sucks you in.
It's not NFS or Ridge Racer style game. PGR3 combines simulation and arcade racing. If you want to win, just don't hit the sides of the track. Like I said the game can be very irritating sometimes, when you need to collect points in cone challenge or when AI car hits you and you loose control, speed and... platinum medal...
Multiplayer:
People still playing PGR3 and that's great because on-line racing gives you a lot of adrenaline and fun.
Overall:
PGR3 is good for sim and arcade racing fans, but for the firsts it could be too simple like for "arcaders" too hard sometimes . There are lots of great cars in the game, they are all different.
It's 2009 but still it's fun to play PGR3 and you get a lot of fun and positive emotions. Multiplayer is also very good.
Before you buy PGR4 it's worth to try it's predecessor.