Offline died very quickly for me, offline is a case of earning money and buying the cars that i want, nothing more.
Online on the other hand in my mind should be treated as a sand box in which you create your own events, or sub games like dirty team races or cat and mouse etc. etc.
How good that sandbox is comes down to A: your imagination and B: the guys you play with, for a start half of GT5 for me isnt the racing game itself but the competition of beating the skilled racers i race with.
Try No aids and abs 0 , the game comes alive.
In the league i run in we match groups of cars to be a lot closer than PP can manage for league races so that cars that wont normally work together now do, testing is a pain in the butt, but its all worth while once you get a cracking race out of it, these are the things that keep GT5 alive for me.
Having said that it does lack quality DLC, its odd they dont seem to want to milk it more.
P.s. I dont own a "PS3" anymore only a "GT5 player"