A GT5 technical and a gameplay thread wouldn't be a bad idea.
As long as you didn't think photo and replay mode were going to be actual game play, you shouldn't be disappointed with the visuals. It's still the standard for visuals in a racing game.
My biggest concerns are:
1. Framerate. Prolouge was not acceptable to me. I want to see how GT5 performs with 16 premium cars on track, running in close quarters on a busy map (like Monaco or london).
2. Grinding. Forza 3 was amazingly bad at rewarding you for playing! The credits you acquired vs the costs of the high end cars was terrible.
3. Online. Not much to say here except don't do a Turn10.
Did you play GT1 2 3 or 4? unless something drastic changed since those then getting cars can be done in several ways, including grinding if you really "want to". Sadly i have no idea of how it worked in FM3 and it´s out of the scope of this thread anyway since it´s GT5.
Same goes for FM3 online, but in regards to GT5 Prologue, i found it piss poor. But the announced track days sounds pretty incredible and more than i would have hoped for.