I've found Ghoul's touch to be, by far, the most useful/powerful spell in the game. This last time around, I used it to kill the Balor (paralyzed then coup de gras) and Z (same thing. I saw a message saying she was immune, but then it listed her as "held.") Is the spell really supposed to be this powerful? It seems as if it always works.
Never really tried the spell myself since I have no desire to have my wizard get within melee range of anything but I would think that any low level spell that causes immobility/inaction on the part of the monsters (Stinking Cloud, Hold Person, Tashas' Hideous Laughter, etc.) would be considered overly powerful...