Finished it over the weekend, I enjoyed it. Takes some a few episodes to figure out the world but it didn't stop me from liking it.
They fumbled there but after reading that all three of the storylines are separate books (The Crows coming much later) and they put them all together made somewhat sense. None of these Netflix shows are guaranteed multiple seasons like network TV, so they had to keep new and old fans interested. But I still didn't like how they handled it.
In for season 2 though.
Nina and Matthias' story is pretty much directly lifted from Six of Crows. They're flashbacks in the book. Nina isn't actually featured in Shadow and Bone's trilogy but in the Crows duology and the King of Scars duology she's a POV character in both so pretty important.
Considering there are 7 books in this series there's enough content for at least that many seasons of this series. Given she's a POV character in 4 of 7 books she's probably the most prominent character in the series.
There's another character that's featured in Shadow and Bone's last 2 books (not POV though) and is a POV character in the King of Scars duology that's the only other character featured as heavily in the series overall than Nina.