I still remember getting my Dreamcast and getting Sega GT. My friends were playing Gran Turismo and I had Sega GT and boy I loved it more than Gran Turismo.
I thought the true gems were Test Drive Lemans and Ferrari 355 challenge. Test Drive Lemans was a Great racing game with some of the best graphics on the Dreamcast. IGN did a story on it back in 2001 I believe and the Melbourne studio said they programmed it in Assembly to extract as much as they could out of the Dreamcast. F355 was not slouch either. There are other great racing games on the Dreamcast but I can't personally say Sega GT was one of them.
Didn't they basically take the arcade version and put it on a disc? I vaguely remember reading somewhere that the arcade hardware was very similar to the Dreamcasts hardware so it took comparatively very little effort to port it over.
The last one I remember buying was Metropolis Street Racer - good fun.
If you haven’t checked it out, give Tokyo Xtreme Racer a look
I found most of the Dreamcast racers seem to fall short in significant ways. Whereas the Saturn had games with more polish. Which is weird because the Saturn was not a good console for fast 3D graphics, technically speaking. Manx TT is up there as one of the best motorcycle racers imo