Ishar 2 & 3 were nearly impossible (IMO). The clues were almost impossible to find and for some of the puzzles you had no clue at all. I finished Ishar 3 with a solution at hand when I got stuck... (did the maps myself though). Plus the fact that in the beginning you are just walking around beating up ninja muggers just to get cash and experience was not exactly fun. But I did like the character system those games had, like the fact that different characters could have relationships or hate eachother and disappear during the night.
Dungeon Master was indeed my favorite Amiga RPG. It was hard, but possible. I liked the way you developed your spells, although there was a lot of training required for that game also to get the spells to higher levels (I know I kept a huge amount of potions for it
). The same system still applies today to games like Morrowind. And then the way you had to kill most enemies in the beginning of the game. Either jam them between a door or toss your entire collection of clubs at them