I suspect you'd change your mind if you sat down and resolved to play one, particularly the first Dark Souls with its consistent, interconnected world. There's something very compelling about a game that throws you up against absurd giant bosses armed only with the mechanics you learned in the tutorial and never cheats by resorting to quick-time events or other gameplay gimmicks. There's no sleight of hand and what you see is precisely what you get. It can be infuriating, but the game does its damnedest to play "fair" throughout.
It's hard to explain to someone who hasn't experienced it for himself, but there is something really worthwhile there. Difficulty is vital to the experience, but it's not just a masochistic novelty like, say, I Wanna Be The Guy or something.