Witcher's based on the same game engine as NWN, no? That being said, I can't remember any bugs in the Witcher, maybe two or three CTD's in a year and a half of playing. Load times are nothing either (in EE at least).

Never played NWN, so I can't really weigh in on that one, or on what the worst RPG is. Like most bad RPG's, I played the demo and then forgot it.