Most are quite easy, but a few have given me fits. Slalom is usually my weakness, but I golded IB-1 within 3 tries.
Golding IB-3 (Mustang at Willow Springs) just about made me pull my hair out! That 'Stang is such an ill-handling brute. And yes, I drive on a DS3 with all aids off except ABS 1.
I think that the challenge licenses once provided have been replaced by other aspects of the game. Such as Goodwood, Mission Races, Karts, etc. Kart Cup 100 @ Space I has by far been the biggest challenge I've faced so far. Let's just say I'm glad restarts don't affect your W/L record!! Not to mention Lunar Mission 3.
Though, I have been reading that the S-Licenses are pretty absurdly difficult. Not looking forward to the Veyron @ Ascari for S-License when I reach it!