Of the three original Secret Circle books, this one was definitely the silliest.
The "big bad," Black John's plan for fighting the Circle was installing himself as principal, creating a new list of rules (ex. no smoking or cutting class), and selecting student "hall monitors" to enforce these rules. The main characters all react to this with such over-the-top seriousness, complete with Nazi comparisons (yes, really), that it's hard not to giggle or shake your head a little during these scenes. Cassie being sent to the principal's office is written as if she were being shipped off to await the guillotine, with the rest of the Circle conspiring to spring her out.
Black John is a fairly enigmatic villain whom we never learn much about, beyond the big reveal regarding his relation to Cassie. I'm still not quite sure what his actual objective was, or how he managed to come back to life besides just "magic." I also wish we had gotten more backstory about how he swindled the last generation of witches in New Salem. At the same time, it was nice to see Cassie grow a backbone in confronting both him and Faye, whose presence in this book was arguably smaller than in the previous two.
The actual prose of The Secret Circle has been consistent throughout the entire trilogy: clear, concise, well-paced, and engaging. I don't think I'm the only person who believes that YA hasn't been as strong for the past few years overall, which makes this series by L.J. Smith--a writer-for-hire who was eventually replaced by a ghostwriter--so refreshing.
I do wish we were able to see more of the supporting characters in The Power; the heart of this story has always rested in Cassie, Diana, and Faye (who, in a clever twist, form a triumvirate to lead the Circle by the novel's conclusion), but I missed the bonus scenes with brilliant Melanie, coy Suzan, fiesty Deborah, and compassionate Laurel. Aside from one bonding scene between the seven girls--where we're treated to more of the excellent symbolism that is sprinkled throughout the trilogy--the story is largely overshadowed by treasure hunts and boy drama.
Nick is finally given more room to shine, but his role in The Power is largely limited to a short-lived romance with Cassie that neither expects to last, even though the two have much more chemistry than Cassie and Adam (although both pale in comparison to Cassie and Diana, which we'll get to in a bit). Nick handles rejection well, and Cassie is free to pine after Adam, who still hasn't been given any depth over the course of three books.
There's remarkably little spellcasting in The Secret Circle, but the third novel's climax is enough to make up for it. I loved how much thought was put into the mythology of the story, and how so much of it--the stones, the rituals, the paintings of goddesses--is used to symbolize each specific character. When the Circle casts their climatic spell, each contributes a line that reflects on their character (fire for Faye, ice for Nick, earth for Melanie, etc.), and it added a depth to an otherwise straight-forward story.
I was genuinely surprised by the reveal that one of the witches had unwittingly been assisting Black John all along, and I liked how everything tied together in the end. Smith left plenty of open room for later installments, such as the acknowledgement that different families could have an inclination for particular powers, and the possibility that Diana and Faye are each one-half of the reincarnation of a Puritan witch whose soul split in two (!). There was always an element of mystery and elitism to the Circle, who ruled the town through the sheer power of everyone else being intimidated by them. In The Power, we finally see the Circle reckon with their reputations, and agree that it is past time to make amends.
The weakest part of The Power for me was, as always, the romance between Cassie and Adam. As mentioned before, Adam is given remarkably little character development, and any person reading this series today would come away believing that Cassie was actually in love with Diana, not him. And while the teenagers of The Secret Circle have never been particularly realistic, Diana lovingly handing Adam off to Cassie in front of everyone else was just too unreal to be taken seriously.
All in all, I thoroughly enjoyed this series, and hope that it continues to find new fans in the years ahead. I look forward to reading the sequel trilogy and seeing how it compares to the original.