Finished this recently. Thought it was entertaining as hell. Never read or heard of the book so I don't know how close this was to the source. This was better than The Wheel of Time.
The author basically threw Ocean's Eleven, X-Men, Gotham (tv show) and Game of Thrones in a pot and let it cook.
I haven't read all of the main series but, I did read the sequel series. From my side, it looks like the show is combining the sequel book series with the main book series. In the books, the main series is focused on Ravka which is an amalgamation of medieval Russia/medieval Eastern Europe which is why you see those cultural aspects in the show. It's cool too see because there aren't alot of shows that depict Russia/Eastern Europe like that. The sequel series is set in Ketterdam, which is like Gotham/Las Vegas/Amsterdam put together. There's less magic involved in the sequel (its still present) as the story is more about the criminal underworld of the city and the devious shyt they get into. In the books, Inej, Kaz, Nina and Helvar don't know who the fukk the other characters are because they're busy with their own shyt. I'm sure they'll do some Daenerys/Jon Snow type shyt and have both groups eventually meet up though.
They did a good job casting Inej and Kaz also. Spot on imo.