If you watch the polish series today as I did, without any nostalgia most fans seem to have, you'll notice a lot of issues. Given the small budged and time when it came out, I'd fully excuse the funny practical effects, and perhaps even the weird choice to have the witcher carry around an eastern katana-like sword. Back then it was probably cool, so OK.
The Series, as the Netflix Adaptation, is best when it sticks to the source material as close as possible. The stories about the first encounter with Yen, the Striga or the Devil are all good. My issues are with the themes the series decided to introduce. You can pretty much skip the first two episodes and you'd be better of doing so. For some reason Kaer Morhen is depicted to be a quarry, even though there are loads of castles they could have used in Poland (and in fact, they feature castles in later episodes). More over, there are a lot of Witchers and for some reason, they claim not to have any feelings while Geralt is wrong for having them (although every witcher gets visibly emotional multiple times in the episode) and for some reason, they don't know what a woman is? The depiction of Kaer Morhen, Vesemir and the new themes introduced by the series are nonsensical and should have been left on the cutting floor. The Polish Series however manages to stick to the books more often than not, and as such is superior to the Netflix series. Dandelion/Jaskier is painfully miscast, but Zebrowski does a very good job as Geralt. All in all, this isn't an essential series every fantasy fan needs to see, but to a Witcher fan I'd say it is a pretty inoffensive fun adaptation. You'd still be better off spending your time listening to the audiobooks instead though.
