I died, as a beginning Wizard, to that guy that attacks you in the barracks (or the building beside the barracks?) in Candlekeep. This was on BG:EE (I say that because I'm not sure of all the specific differences)
My character missed with his quarterstaff attack about 13 times in a row, and the foe easily dispatched my 4HP in that time.
I don't really count that as difficulty, as much as just lameness.
I think BG1 was the perfect example of bad difficulty. Everyone had so few health and AD&D 2nd Ed was set up in a way that one hit could instagib a character and lose them forever. There were also no special abilities so it was literally just roll and hope for the best
However when you got to BG2 you had more at your disposal so it was generally a lot better. If only BG1 was like that level - still challenging but not entirely down to luck.
The systems in KOTOR and DA were also good - low levels were interesting because you had abilities to use if you weren't a spellcaster, and things could be challenging without being unfair and relying on luck. However the mage battles were less indepth. A combination between BG2 for late levels and early levels like DA and KOTOR would be perfect for me.