Yeah, okay, I'm the last person to buy GT3, weeks before GT4 comes out. I had GT2 for the PSX, and played it more than any other PSX game. And that was even just using the normal controller. GT3, as you'd expect, has much better graphics, but so far (I've run 3 races so far), is better on gameplay as well.
Let me say that I'm not all that experienced with driving sims. I've played a couple of the Need for Speed PC games, as well as Colin McRae Rally on the PC. They're all acceptable to my tastes (although CMR's replay is fairly poor, the driving was fine to my uncultured eye). So the feel of the cars isn't something I'm going to notice much about. GT2 was fine, GT3 is as well.
But there are a couple of other nice things about GT3. First, you can qualify for starting position. GT2 always started you out dead last. Okay, fine, I could usually get up to 1st or 2nd place by the first turn. But getting a couple of laps on a new course and using that time to get started ahead of the pack is pretty nice.
The menu layout is less chaotic as well: I can find things easier in GT3. It could be a little nicer, I think, but it's still pretty decent.
Okay, let me oooh and ahhh over the graphics. While you're racing, it's considerably nicer. There are pieces of animated eye candy while you're driving that are amusing. But when you start the game up, there's a segment of video that plays (along with some annoying theme music), with actual races. Pretty cool by itself, until you realize that some of the clips are from actual races, and some are from the game itself! Replays of the races are quite high quality, and while you can tell they're generated, it's only little things that give it away. Oooh! Ahhh!
Yeah, I'm going to play GT3 for a while, until GT4 comes out and the price comes down. And I ordered a wheel controller, too, to make playing it a bit easier and realistic. Way fun stuff.