The vibes I get surrounding the GT3 vs GT4 are similar to what I've experienced, GT3 is good, but it feels like a PS1 game, GT4 seems like a fully fledged PS2 game, a cutting edge one at that (as it should be, near launch title vs. end of life title), and I'm not sure about the cars, but I'm convinced the scenary in GT4 is better, as others have said, the vibrance of GT3 actually works against it, on older television sets, the move to GT4 might've looked darker, and hence the improvements would've been noticed less, but when using a large screen, with an RGB cable from the PS2 (and that makes a massive difference on its own), both games running as high as they can (PAL), I think GT4 is improved on GT3, in a big way.