Actually, as someone who enjoyed the shows, I'd be interested in how they deviate from the novels.
There are some intense character changes that almost amount to character assassination. When you look at how Yennefer in the books, she is a little harsh, but ultimately a very caring mother figure to Ciri, whereas in the show they concoct a plot of her losing her magic and wanting to sacrifice Ciri.
I get that they wanted to add a plot line so that yen had something to do, because in the books she is not the point of view character, and so you just hear about what she's up to, instead of seeing it directly, but when they wrote a plot for her, it did not match her characterization in the books.
Then there are world building faults, like how people travel across the world really fast by horseback. Like, there is this really weird scene where geralt and yen reunite, and it's really far from Kaer Morhen, and yen rides away, and Geralt follows, and the next time you see them they are riding into the castle, and that is the first time they have a conversation about the urgent matter that prompted them to write off, even though it would take weeks to get there.
And they depict the witchers at Kaer Morhen as incompetent compared to how they are in the books. It takes several witchers multiple minutes to just hold their own against some monsters, whereas they're supposed to be pretty badass, and should have been able to take on those monsters much faster, maybe even solo.
It just feels like the writers didn't think the original books were any good and so decided to change stuff, rather than try to give fans something that matched the stories they liked.
And even if I'm open to adding stuff to fill in gaps, they did it in a way that messes up characterization and threatens to make it so great parts of the story later on won't fit. A mean and heartless show Yen wouldn't protect Ciri the way she did in the books.