I loved Poison Study. I enjoyed Magic Study quite a bit, but not as much. Fire Study was overall disappointing. 
 The plot was all over the place and very confused. The first half was chasing a group of people who constantly changed numbers. It was boring. After the halfway mark it did pick up and became a lot better, but was still lacking. I felt like the ending was really rushed and didn't entirely make sense. I was disappointed that one of my favorite badass couples had a very stupid fight. Le sigh. Even the writing felt...not as good as it had previously. It's been a while since I've read the first two, but...yea. 
 It wasn't terrible. I was sucked into the second half and I still love the characters. I hear there's going to be three more books and there's a good chance I'll check them out. I also plan on reading the trilogy about Opal. I'm just kinda bummed that this book really didn't deliver. Poison Study is honestly one of my favorite books. It was near perfection. If only that magic could have been there for this one (Magic Study could be better too). 
 Ah well, I'll always love Yelena and Valek.