I like the series. The dialogue is not nearly as good as in the short stories/books, and some things are left out in a way that I find absolutely infuriating.
But when I approach it as its own thing and don't lean on my memory of the source material too much, I find Witcher to be a rather good, if not spectacular, series. And I was a pretty big fan of the books/stories, and I loved the video game series (especially Witcher 3)
(I do recommend the books and especially the short stories to anyone who watches the show and likes it. It's much wittier and funnier in my opinion, and has snappy dialogue. Keep in mind that the books are two decades old by now, short stories are even older, and they're all a product of their time. Plus, I have no idea how good the translation into English is)
EDIT: spoilers for the first episode (and more importantly, the short story it's based on) below to illustrate a point:
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In the short story the first episode is based on, Renfri is very clearly a dark take on Snow White - complete with a version of the seven dwarfs (I don't think her crew are dwarves, but there's seven of them IIRC). There are multiple allusions to just about every part of the fairy tale. It's not exactly subtle, either. In fact, almost all short stories involving Geralt are dark or humorous retellings of classic fairy tales, and it's a big part of the appeal.
If I didn't know that, I don't think I would ever have guessed Renfri is supposed to be Snow White. I am not sure why the series almost completely ignores this, as it's a defining aspect of the franchise before the novels were published. Maybe it's the fact that there have been dark takes on Snow White (and other fairy tales) since the short story was published, and people unfamiliar with Witcher would think the episode is a rip-off of those, despite being based on material from decades prior? No idea.
EDIT 2: this is very subjective, but while I was sceptical of the casting of Cavill, I think he pretty much nails Geralt as a character (better than the video game version's actor, either in the Polish version or the English dub). He is the perfect emotionally stunted asshole that book Geralt is, IMO.