This has been a disappointing end to what had the potential to be an awesome series. Perhaps Poison Study should have wrapped up neatly and been a stand-alone novel. After reading Magic Study and Fire Study, I feel as if they were superfluous, and actually don't add much to Yelena's character. 
 I was a bit tired of this long-distance 'love' between Yelena and Valek, since they almost never saw each other. 
 I was also not enamored of the plot, especially of this book. It felt fillerish and caused Yelena and other characters to do very stupid things you wouldn't see anyone with a modicum of intelligence doing, just so the story could be moved along. 
 I mean, for those who have read the books - how stupid does one have to be, to not kill Cahil after his constant foolishness which ends up putting people in mortal danger? How stupid does Cahil himself have to be, to go about every single time,hanging out with fools and murderers and doing horrible things (beating Yelena) and then realize the error of his ways and come asking for forgiveness? How stupid do you have to be not to know that the people you are hanging with are not good when they're capturing people and killing them for blood rituals, when even children are included among their captives? Just petty stupidities like that - from Yelena, Lord Marrok...just about everyone except Valek. 
 I felt this diluted the quality of the characters, after all, they can't be so great if they're so stupid, can they? And I do think somewhat less of Yelena now. Valek, and perhaps, Ari and Janco, are the only characters whom I felt maintained their integrity. 
 If Maria Snyder had stopped at book one, or come up with completely different plots for books two and three, she might have had a proper winner on her hand. 
 I read somewhere that someone read somewhere that Ms. Snyder had originally intended Poison study to be a stand-alone novel, and wrote it accordingly. But the publisher had wanted more than one book (prolly to make more money) and so she'd changed the ending to an open-ended one and come up with this trilogy. If that is the case (and I can certainly see how that could have been the case), then it's a major fail on Ms. Snyder's part and the part of her publishers.