Have to agree with the OP, I am tired of dark fantasy, and I do not think that The Witcher series does it well either.
The character still speaks as if he smokes 40 a day, is constantly frowning(in fact, a lot of characters only ever frown, aside from Dandelion and maybe a few dwarves), all of the women in the game are sexualised to one degree or another, if not also abused.
Oh, and the constant swearing.
It just becomes jarring and ultimately boring to have such a bleak world, yes, I understand that the "your role in the grand scheme of things is tiny anyway" thing is done well, but that doesn't add into a game being a good 'dark' fantasy, but it having a more realistic outlook on things.
All the other thematic elements still feel juvenile, even if there are in-lore justifications for it.
To be honest, I felt that Dragon Age 2 was done better at least in theme than Dragon Age Origins: the addition of the glib remark, Varic, Merill, Isabella, Aveline acting like a schoolgirl when trying to romance someone, those were all welcome additions to the game, as they made it less boring than its predecessor. DA:O did have its moments with the mabari, Alistar, Morrigan, Oghren and Shale, but they were few and far between(especially when Alistar started being all sad about his heritage). Also, the world was a bit too grim-dark at times too.
I personally think that Game of Thrones does it best because it paces itself a lot better, and that it still doesn't go completely grim-dark(there are some genuine moments of joy and a sense of "maybe things aren't as shit as they seem"), or rather it manages to balance things better.
Or maybe its just Tyrion.
Yeah, it's because of Tyrion.