Never played Gran Turismo 2. I've played GT1 and for me it wasn't that hard most of the events, yes from GT3 and up it started to get hard:
GT3 Licence S-6 : Viper Team Oreca at Laguna Seca - Got gold on 3rd try... Come on, this wasn't hard...
GT3 Licence S-8: Toyota GT-One at Monaco - Took me some tries but it didn't take that much time. Managed to get gold as well.
GT4 Licence IA-16: Nissan R92CP at Le Mans - Gold on very few tries as well. It wasn't hard either.
GT3 Time Attack 10: Ruf RGT at Complex String - This took a while for me because I never used this car and I didn't like it either, but I took less than 10 minutes to clear it. Medium at best, definitely not hard.
GT4 Mission race 23: Nissan Skyline at Test Course - Gold on 2nd try. Maybe it was because I saw a friend completing this mission before. But it also didn't look that hard, you just had to time correctly your splitstreams.
GT6 GT Academy Final Round: GT3 GT-R at Spa - Very few tries to gold it as well, I love Spa, one of my favourite tracks, and I also liked the car.
GT6: Licence S-5: Veyron at Ascari - This was HARD???? Gold on first try and by like 3 or 4 seconds. Maybe for those who aren't used to drive the Buggati it's tricky, but believe me, it is that easy...
GT4 Peugeot 206 Cup - When I saw the AI in this Cup at first I knew I had to tweak a bit my 206, but it was still challenging, not so hard, especially if you compare it to the Opel Speedster Trophy one, now that was a b**ch to clear.
GT4 Formula GT World Championship - Easy... It only takes some time, but even in B-Spec you could win most of the tracks and outrun the AI.
GT5 B-Spec events at Monaco (lol) - Yeah, namely the one where you need the Chaparral 2j to win, he at first always crashes in the corner after the tunnel or the last corner, dunno how I won that one, guess I was lucky, because no matter how I handled my driver(cooled him down or not) he always seemed to crash, luckily at one point he didn't crash...
Now to the real challenges that are forever marked in GT history.
5. GT5 Alfa Romeo 8C at Eiger Nordwand - Took me more than like 20 tries at least, and close to an hour straight to clear it, and even so it was by like -0.020 or so from gold. Never did it again after.
4. GT6 Ayrton Senna Brands Hatch Lotus 97T - Took me more than an hour to gold it... I was getting frustrated a bit at how many times I scored silver at like less than 0.100 away from gold. The degree of difficulty of this one was similar to the Alfa 8C at Eiger in GT5, just a different car and track. Also never tried it again after golding it.
3. GT4 Opel Speedster Trophy - I swear, I even had to cheat(crash against the AI, out of frustration) to win some of the races, and even had to ask for advice on how to tweak the car to be able to beat them, after that it was way too easy, like any other normal race. But if you don't know the formula(to tune your car and tweak) for this CUP, you just can't win(clean that is) this, the AI look like GT pros this time.
2. GT4 Mission race 34: SLR at the Nurburgring - For starters, I played the NTSC version, yes, the one where you start at around 2:03 minutes instead of starting at 1:54 which is the PAL version, in which I have seen videos of guys overtaking the 300SL even before the end of the Nurburgring straight. I guarantee you, in the NTSC you are not going to overtake the 300SL before the 2nd to last corner, and you have to to be very, very good to overtake it in the last corner. I overtook the 300 SL even AFTER the last corner, we were already in the mini-straight for the finish when I passed it, and this was after like 10 hours AT LEAST. It took me 2 days straight to finally complete this. And the biggest frustration was to wait 2 damn minutes every time I restart it. Truly worth it of the final mission. What drove me to complete this was the fact that I was a big SLR fan(still am) and I really wanted the car prize Nissan 89C(was it?) for my collection of cars.
1. GT5 Sebastien Vettel X challenge: Nuburgring GP - ... To gold this one it took me around a week... And am going to tell you straight away, you cannot gold this without the patch(no, not the patch where it's added a few seconds, it's before the patch where they finally add SENSIVITY to the controller), seriously without Sensivity I just couldn't get anywhere near gold and I struggled days to get silver... That's how hard this was. Even with the sensivity patch up(used sensivity 7), it still took me some hours to gold it, but silver was easy this time.
And now for the King:
0. GT5 Sebastien Vettel X challenge: Suzuka - Contrary to the Nurburging GP challenge, in this one, even after the patch, even with the controller at sensivity 7 I just could not get gold, it took me weeks to get anywhere near gold and I even stopped to complete other events of the game, and when I returned to complete this one challenge into gold, the final only one left, I took another few weeks to gold it... It was just ridiculous, it was like this event was designed for controller users to not gold it. Can't even remember how many times I had to get into the grass/sand, crash to finally master every turn of the Suzuka with this car using the controller... And that last corner... how many times did I failed at doing it perfectly because of how nervous I was to finish it... Going to be modest here... It took me like a 1000 tries to gold it, and again, am being modest here, I think it took way more than that, I restarded alone like 100 tries just from going into the grass in the first corner or breaking too much before taking it... I just had to do it perfectly, you LITERALLY cannot do ANYTHING wrong at all in this event, you have to be perfect in everything, BRAKING, TAKING TURNS, ACCELERATING, SHIFTING, EVERYTHING, and above all else, have the PERFECT TIMING. And yes, I managed to clear before the patch where they add a few more seconds, and after that it wasn't hard.
PS: All of GT series I've played with a controller, never tried or had the money to use a wheel.