Have been playing Forza Motorsport for the OG Xbox and in my opinion it holds pretty great, Microsoft placed many chips on that game and it turned out as timeless gold. When i get a new pirate Xbox 360 i will play the shit out of 3, then maybe try 4 again.
OG did have varied motor sounds, it's there but the audio mixing makes them hard to differentiate, seems it was made for a surround system rather than normal stereo TVs.
Also some unique cars, miss the Tommy Kairas and Veilsides more than i would like to admit. Plus the very rare TVR Typhoon.