I downloaded Prologue from the PS store. I've never played a GT game first, Prologue is my first, and so far, I'm very impresses at some things...not so much at others.
The tracks themselves, aren't that great looking (except for the one in Switzerland), especially the trees and the landscape. They actually look like something from a PS2 or even PS1 game..the trees are just flat :|. I was expecting something more here, especially after the reviews.
The cars, on the other hand, look photo realistic...absolutely stunning. Each one drives differently, and feels different, which makes each car you get a new experienced, so it's just something that's faster, it's something entirely new.
Online is below today's standards. You can't match up with friends, and you can't customize the event at all. I hope it's improved in GT5.
Also, I heard that in other GT games you could customize your cars. Why can't you here? This is supposed to be an EVOLUTION- something BETTER. As you can't customize, if you have the fast car in a race, and if you start off in first place, you will win, even if you're not that great of a driver.
Overall, the game is great fun, but there are some problems, as I mentioned. I think it's very overrated.