I'm pretty peeved about this. As a long time Witcher fan (played all the games, read all the books, etc) I have a few issues.
Hopefully there will be a canonical reason for this, but:
1) The witcher medallion looks nothing like it should
2) Where is Geralt's second sword? It's literally a staple point of the series
3) Showing Yen before she used sorcery to change her looks kind of ruins the illusion. They never showed it in the games or went into detail in the books for a reason. (personal gripe, fine)
4) *Disclaimer: I'm in no way getting into racist territory here* The casting choices are very poor. It is a Polish folk-tail, i.e. Slavic mythology, setting, etc, yet they had to shoe-horn in actors of nationalities and races that simply do not fit in the Witcher universe. There are other characters that come from other parts of the witcher continent that would make sense to be from different races, heck, even bring in new characters if flexing political correctness is that important, but damn.. to take main characters like Triss, Yen, and Fringilla, who the BOOKS DESCRIBE the appearance of, and change their races to fit some agenda, is simply not sticking to the source material, to the point where it makes NO thematic sense.
5) The Nilfgaardian armour looks like trash, not the proud black and gold it's meant to be.
There are aspects I do like, so I'm trying not to cr*p all over this.. e.g. I think Henry will play a perfectly fine Geralt, but I just really REALLY don't want Netflix to sully my favorite series of all time.