It's one of my favorite racing games ever. I had a twin for ~5 years, and played a ton of it (was my go-to for a break from studying for tests in college)... it took forever to get really good at it, though I did eventually get to where I could almost always win the race. Everything about the game is really well polished, even down to the realistic force feedback effect when driving over cobblestone on the one track, but it's definitely still "arcade-y", so it's fun even for beginners (unlike something like F355 where it's almost too much simulation for casual players). And IMO, the graphics are beautiful, even today.
I did eventually sell it to make room for a pair of SF Rush the Rock, then Rush 2049 and Hydro Thunder. Those have a lot more secrets and stuff that give the game depth for both beginners and advanced players... so I'd recommend those if you're looking for something with more adventurous replay value, but Super GT has plenty of replay value if you enjoy honing your skills, figuring out the optimal path for drifting corners, etc. And in setup, you can even set it for "endurance mode" with a bunch of laps, making pit stops, etc.
DogP