My GT experience started with GT3. I never owned a PSone but bought a PS2 in 2001 (I think, back when they were still hard to find in stores). I bought Gt3 shortly afterward. So I've played GT3, pretty exclusively (I rarely play any other video games than the GT series) for 3 or so years.
Recently I bought Gt2, wanting to see what all the fuss was about and to drive the RUFs in the game, mainly the "Yellowbird", and some of the circuits not in GT3 (autumn ring, rome - night, GV east). I've been playing it for about two weeks straight, completing everything beyond the make(s) series, which I have little interest in completing given all I wanted to drive were the RUFs and maybe a BMW or two.
I gotta admit I don't care for GT2 much. I expected the graphics to suck, though honestly given it was meant for a PSone it seems impressive and after a few days you don't even notice how them, though I felt like my eyes were blurry all the time that I wasn't quite seeing everything..hahaha.
The gameplay is, ummm...too complicated, the tuning makes little difference, the race mods (big deal) and in general I prefer the simplicity and straight forward-ness of GT3.
Maybe if my GT expereince had actually started with Gt2 I'd feel differently. I am glad I bought it and have experienced it but I don't see myself playing it much more. I'll finish up GT3 for the last time and work on my ultimate SIM garage (which I plan to offer for download on this site in the near future, more about that later...)