Regarding the personality of Nibenay, we know precious little about this enigmatic figure. Yet he is given special attention by our authors. From Troy Denning, he receives a powerful cameo in Amber Enchantress, and Simon Hawke makes him the master antagonist in The Wanderer. Happily, Hawke seems to seemlessly follow Denning’s vision of the Shadow King. He is enigmatic, calculating, remote, and very pragmatic. He offers very few secrets about himself or anything else, despite the surely dizzying amount of lore he has gathered to himself across the millennia.
I would not say that Nibenay is “disinterested.” Rather, he is very interested, but only insomuch as the matter has to do with him or his city. I speculate he has developed over the many centuries a considerable dedication to his city. It is first and foremost his base of power, which he has very much required so as to maintain his status among his peers and to fuel the Prison. But I also suspect he has a more personal dedication to the city itself and his people. For the city he seems to have considerable pride. It is his, is stamped throughout with his face and presence, and is among the greatest remaining cities on Athas. As for his people, I actually suspect a considerable percentage of his subjects are actually to one degree or another his own descendants. Whether due to pleasure, policy or both, he has likely mated with many thousands of virgins throughout his reign, many of which were already of his blood, and thus the city of Nibenay may very well be Nibenay in a way that is fairly unique among the cities of the Tablelands. As a measured pragmatist, Nibenay has little compunction of punishing or even destroying particular members of his own progeny, but he seems to have favorites that he protects (Prince Dhojakt), and surely his people as a whole are a great and precious asset to him that he would not see destroyed, at least not utterly. I suspect he would differ from Kalak, and would never sacrifice his entire city.
As to sadism, indeed, I think to some measure this plays on his personality, at least more so than with all the other sorcerer-kings. He deliberately generates his mental construct when speaking with Tithian in the deformed shape of Djojakt, as if to disturb and unsettle Tithian simply for the sake of doing so. His wedding night treatment of his templar-wives is also surely unsettling. But all this and whatever other horrors he enacts may not be a matter of pleasure, but one rather of policy. In all cases it could be argued he does these grotesque things to better subordinate and terrify the recipients into subjugated obedience. The templar-wives are likely under no illusion that their husband-king “loves” them and would not destroy even the most beautiful or powerful among them on a whim. Therefore they will always fear him. Any pleasure he derives from such things I suspect is secondary.
As to the new novels, I am thus far unimpressed, though in fairness I have not afforded them much of a chance. I suspect they are largely a “hot mess”, though with their moments to shine. As I have argued elsewhere, I deem that “demons” are inappropriate for Dark Sun, and therefore deny the premise. Nibenay might be much removed and even aloof from the events of his city, but he is surely not ignorant of events that are worthy of his consideration. Beyond the Prism Pentad rightly made clairsentience his foremost psionic discipline, and from time to time I imagine his cosmic awareness folds outward across the city in all-encompassing embrace. Though he would rely on his templars, military and other agents to deal with most issues, should any serious threat come his way, I have ever confidence Nibenay would deal with the matter personally, though his methods may not always be as direct and overt as we would expect of more forceful tyrants.
The gnomes are a furtive and hidden race, that likely did not often face Nibenay’s forces openly in the battlefield. Nibenay would have had to learn how to be clever and scheming to annihilate such a race completely, which he obviously did. I would expect such methods to largely remain the same, though now with arguably the greatest army in the Tablelands, second perhaps only to Urik’s legions, he also is more than prepared to meet threats outright and openly with direct and overwhelming force.