Yeah the games incorporate a lot of the history and lore of what was established in the books and move it forward for their storytelling.
In the books, the monster world is in decline. That doesn't seem to quite be the case in the games. It seems the Witcher world is more in decline than the monsters who seem to still be quite plentiful. I mean, Geralt doesn't have a ton of trouble looking for Witcher work from town to town.
I think Eredin's motivations in the books are slightly different.
Also in the books, the Witcher signs are in there, but they are a little more frequent and way more powerful in the games.
Geralt is a little more emotional and philosophical about his lot in life as a Witcher. He has a lot of self-loathing. Geralt is different from other Witchers in that they aren't really supposed to display their emotions, but Geralt is actually very emotional. He broods way more in the books than in the games.
His emotional state can likely be attributed to him having a very powerful lineage. His mother was a druid priestess and a sorceress. His father was a strong warrior. So, even without becoming a Witcher, he had a strong bloodline and probably could've been easily raised and bred for combat.
Geralt had a lot of early success in the Trial of Grasses, better than most. So the Witcher mages did even further experiments on Geralt, which is what caused his hair to turn white. Granted, these experiments are brutal, and the survival rate on the children forced to undergo them are minimal. That's probably a big reason why Geralt has sort of an honest, self-loathing view on Witchers. It's not exactly an honorable profession or group.
A part of me wonders if the unconventional experiments Geralt received allow him to experience stronger emotions than the other Witchers who have better control over their emotions. On top of that, I suspect his strong genes might also have allowed his emotions to come off as more human than other Witchers in general.
