The game has entirely too much grip if you compare it to the newer ones. Strange to notice now, because back then it felt entirely life-like.
I never made the mistake mentioned in the first post, because I never would assume a gear chart reading would automatically come true irrespective of vehicle power.
I think the biggest disappointment for me, back when I first got it, was the complete lack of Euro/US rides. They focused on them more on GT2, and they seem to be again in GT4, so that's good. Some other noteworthy ones are the fact that a racing transmission always kept the stock amount of gears (I want an R32 with six speeds, damnit!), and as SportWagon mentioned, the 12000Cr "issue". What I really do miss however are the gear charts and the dyno readings (when switching boost levels).