Although I just recently got into it, the Witcher.

I was honestly blown away by the depth of lore in these games, and I've been slowly working through Andrzej Sapkowski's short stories and novels. Even with all the material there is now, there is so much to be discovered. I mean the Conjunction of the Spheres is a crazy cataclysmic event that brought humanity to The Continent, but it also brought a whole threat of monsters from different worlds. The colonization of The Continent is actually a huge part of the lore because it plays a huge role in the political structure for the present day Continent. Humans arrived after most of the non-human races, but humanity still managed to dominate. Just the way the whole world is set up is brilliant. The Witchers, the Sorceresses, the Wild Hunt, the non-humans, etc. I could probably go on for awhile about it, but honestly there is still so much unwritten about the world. I think over time if this series was done correctly it could be among some of the great fantasy lores

I would have to say among the numerous politics, and ambiguous morals my favorite part of the lore are the Witchers. They are just the most badass characters. They are usually talked about in the games as monsters or sell-swords, but they are so much more. They endure the Trial of the Grasses, and become so much more than human beings. If a person successfully lives through the trial they then spend the rest of their lives training in their respective styles (Wolf, Griffin, Cat, Bear, and Viper I think). Their knowledge of monsters is unmatched; from their weaknesses to the use of potions to further their advantage on a target. They are the perfect hunters. The politics of how Witchers are "chosen" is wrought with controversy as they usually just take children rather than ask for their permission. The entire witcher profession is one that is necessary(They are pretty much the only ones who can deal with monsters effectively), but at the very same time vilified by a majority of people on the continent. Plus, the wielding of the silver and steel swords is so awesome haha.