I played PG 1 and PG 2- both were borrowed from a friend of mine and i didn't really like them that much. PG 1 I admit was a very nice game of it's time, but i had SegaGT 2002, which at that time was one of the best driving simulators in my opinion. I played Forza 1, also borrowed, but i never actually got into the series till Forza 2 came out back in early 2007.
Like i said a few pages earlier, Turn10 has taken over the Project Gotham franchise and experts say that PGR (4..?) is going to be a game much like Forza. I'd love to see what it's all about when it gets released. I'm all about racing games, and NOTHING else.