This is definitely a "peer-pressure read" for me as I picked it up from the library after reading several rave reviews of it from other bloggers, but it certainly lived up to the high expectations I had for it. I wasn't prepared to enjoy the love triangle, but I think Calla's relationship with Shay was portrayed well and Ren, who was a bit of a stereotype at first, became a more intricate character towards the end of the book. At the heart of the story though is Calla - smart, tough, and loyal - a heroine torn between her own desires and what's best for her family and friends. Despite her supernatural abilities she is an everyday teenager and her struggles come across as sympathetic rather than angsty.
Andrea Cremer has reinvented werewolves with her story of Guardians and Keepers, and the mythology and history that she writes into the world makes it easy for the reader to become enveloped in Calla's story. Nightshade is the first in a trilogy and with the cliffhanger that ends this book, readers will eagerly reach for the second.
I have to point out, also, how much this book reminded me of Matched by Ally Condie. Granted Nightshade is more paranormal where as Matched was definitely sci-fi, but both books deal with a girl torn between the guy that society deems the right mate for her and another who represents hidden knowledge and a chance to question authority. I know these aren't really new themes, but there were a lot of interesting similarities in how they were handled in both books. I don't bring it up as a criticism because I enjoyed both books, but I was curious if other readers of these two works had noticed how alike they are.