My Reaction in a Nutshell: 
 Overall, the most anticlimactic book of the three. 
 The Long Version: 
 This book was much slower than the first two which really surprised me. The Forever Song begins with Jackal, Kanin, and Allie on the hunt for Sarren. Allie, distraught from the loss of Zeke, begins to ignore her humanity she so desperately clung to in the first two books. Rather than grieving, she starts to give in to her inner demon, the monster she fought for so long. She kills without remorse, calls humans bloodbags, and hides all painful memories of Zeke. 
 This book started off great. I kind of secretly love it when the good guys turn into villains, so I loved reading about Allie's moral dilemma. This book, like the previous two, did not gloss over the messier details of vamp life. 
 But that being said, I could predict every "plot twist" in the book. Nothing surprised me. It made the whole story anticlimactic. 
 (view spoiler)[Just a general (but super spoilery) question: After Zeke broke Sarren's compulsion, why did he never ask about his cross? He wore it every day in the previous two books and Allie left it at the graveyard outside of Chicago, but Zeke never asked Allie if she knew where it was. Kind of feel like that's a loose end that needs to be cleared up. (hide spoiler)] 
 The writing was more reflective in this book than the previous two. Allie has longer inner-monologues and there is less action. Overall the plot moved slowly. I liked the first half of the book better than the second. 
 This book falls somewhere between a 3-3.5 star rating for me. I didn't like how predictable it was and the extra focus on romance. It followed a lot of similar tropes of YA which disappointed me. Similarly to the last book of the Angelfall trilogy, Kagawa had a slow plot with a mediocre ending. Plus this book had more dramatic speeches (which I don't like) than the previous two. But that being said, I still enjoyed the book. I love Jackal. I could never tell if he was good or bad or a little bit of both. He provided excellent comedic relief. I want a whole book only about Jackal. 
 Overall, this is still a great vampire series even if the last book wasn't the best. 
 ***TRIGGER WARNINGS: mind control, terminal illness, threat of implied R, kidnapping, PTSD, suicide, death, murder, torture