Gran Turismo 5 Prologue released in 2008, and it was a fair preview for the full game that has been delayed and delayed countless times.

Rest assured, we won’t be just getting more of the same when GT5 finally arrives, confirmed by Polyphony Digital boss Kazunori Yamauchi:

Prologue is really only a prologue. Though the look and feel of Prologue and the full version will have uniformity, the full version will be totally different in terms of scale and diversity in comparison.

So we have been reassured that when it finally does arrive, you can forget that Prologue ever existed!

[Source]