Oh man....
Let's go through this methodically.
GT1 was great, but ultimately quite a short game relative to the others - not this one.
GT2 was a brilliant expansion on GT1, with a stunning selection of cars, BUT:
- it was buggier than a house overrun with cockroaches
- I still think the graphics were just a touch behind GT1
GT3 is visually stunning, with the car physics taking a real step forward (especially for us Logitech users). The game is very deep, although I think it actually lacks the depth of GT2.
GT Concept - far too short a game to be seriously considered, but a handy pointer to improvements for GT4 - the return of old tracks, slightly improved physics and other small changes.
So - to rank them:
- GT3
- GT2
- GT1
- GT Concept
If GT3 had been GT2 (with cars from GT2 and GT3, tracks, and properly enforced racing class rules) with GT3 standard graphics and physics, it would have been incredible - maybe next time...