Yes, there's definitely another series (announced last night). This series approximately covered the first book in a trilogy, so with any luck they'll cover the whole story in the end ...
//I've read the books, which makes it easy to follow even though it's not an accurate retelling//
I thought it was fairly faithful to The Northern Lights, Ellipsis. The only major difference was starting Will's story earlier than before (He doesn't feature until book 2 iirc).
I thought the whole show was wonderful. One of my TV highlights of the year.
I couldn't get into it until about Episode 3, then really enjoyed it all, and am looking forward to the next series. I'm also really enjoying The Witcher, I'm up to Episode 6, and it's all getting a bit clearer now.