Poison Study was a decent story, but I felt like it should have been more. 
 The heroine, Yelena, was pretty tolerable. She's tough despite having some really horrible things happen to her, but not to the point where she always lets her pride get her in trouble. Her talents seem a little unrealistic (practice swordfighting? Sure! Give her two months and she'll be able to take on anyone in the Commander's army!) but if you can get past that, everything's good. 
 The hero, Valek, is the typical tall/dark/handsome quiet badass type. No complaints, except for the way he's introduced. You get his hair and eye color, but you have no idea how old he is until 40% OF THE WAY THROUGH THE STORY. I spent the first several chapters thinking Valek was a 50 year old man, until I realized he was meant to be the love interest and therefore must be closer to Yelena's age. 
 AND SPEAKING OF LOVE INTERESTS! I was actually really frustrated that the characters took so long to realize their attraction to each other. Definitely no insti-love here. I was really hoping for a few cute Valek/Yelena moments, but there really wasn't all that much in the way of that. 
 Plot-wise, it was decent. Nothing ground-breaking. There were a few issues that seemed pretty random and that could have been done without, but maybe they'll prove important in the sequels. Some of the twists were easy to guess. Nevertheless, it was an enjoyable read. 
 Now, this is not a book for younger "young adult" readers. It's not quite adult, but definitely not for the young'uns either. There is a rape scene that, while not excessively detailed, is pretty disturbing. Potential readers should be aware of that. 
 Overall though, good story, and I've already ordered the sequel online.