Why am I expected to be nice?

Gran Turismo 4 takes too much effort to make realistic. Racing with the wheel is decent fun, but not so much as GT5 Prologue, or even GT PSP.

Kaidou Battle is made by the same company as Tokyo Xtreme Racer (and for what it's worth, Tokyo Xtreme Racer X for 360 is pretty realistic too, though there's only about 25 cars...), but it's more realistic in the sense that you're not really creating a drag racer. You actually have to consider brake balance and tires depending on if you're doing grip racing or drifting. Kaidou Battle 3 is the most realistic of all, but I prefer 2 because the drifting physics are a lot more fun. Most importantly, there are a ton of cars and they all drive like they do in real life. A lot of the cars in GT4 are just 'name swaps' (like different years of the same model, and they don't even bother to change the technical details like changes in weight and torque).

And Colors... kind of sucks (for me, that is). It's definitely more for artists who are used to sketching in a sketchbook. I'm not an artist, and I don't sketch. UAPaint is basically like MS Paint for the DS, and it has several hotkeys that are sooooo useful. Unfortunately the guy who made it is working on different projects now, so the few of us with cards that still have that bug are pretty much screwed.

I think I've never tried Kaidou Battle, because I thought it was unrealistic like Initial D, TXR, D1 GP, etc.
GT4 is disappointing if you use the standard settings. It is only understeer, understeer... and all cars feel the same. But if you put the right tires, turn the assists off, etc, you can clearly see the difference between cars. A BMW M5 is very oversteery at high speeds, the TVRs use to be understeery, while a NSX is more neutral and does everything you want it to do.
You can see that I am GT fanboy.

Oh, I thought you had not tried Colors yet.