Played all the GT's (except prologue), even got a PS3 specifically for GT5 - utterly disappointed by it and STILL no S12 in there! The game is just too boring and sterile and hasn't really moved on since GT3/4.
The Forza series (Xbox) are much better games in every respect and you can't beat Need For Speed Shift / Shift 2 for feel and sound - rag a Zonda round the 'ring and you'll be in heaven!
GT5 vs Forza 3 vs Shift 2:
http://www.youtube.com/watch?v=z8zZ2z-nnvY
If you had the cars/features/gameplay of Forza 3 with the sound/visuals/in-car experience of Shift 2 and the multiplayer of Forza 2, you'd have the perfect racer.
Forza 4 due out in October, will hopefully fix the annoyances of Forza 3!