The GTO was a Holden Monaro. The G8 is a Holden Commodore. It is a stretched version of the same chassis.
The build quality on the 2004-2006 GTO’s was far better than anything GM has built in years. They were on par with BMW, Mercedes, & other German makes. The achilles heel was that these cars were/are still sold through GM dealerships. The “american” General Motors does not care about customer satisfaction/service, and this will hurt the G8’s sales. If GM would have the customer satisfaction record of say, Lexus (Toyota), Acura (Honda), or Infiniti (Nissan), the G8 would be tough to beat for the money.
I bought a 2004 GTO new & I loved the car, but could not deal with the poor service (at more than one local Pontiac dealership), and the fact that the Corporate customer service was even worse. I wish I still had the car, but I don’t miss the headaches.