I liked this book about as much as I enjoyed the fifth one. It was easy to read and enjoyable. If I am being honest, I was perhaps a bit sad that just as they were seriously getting better, the series finished. 
 I thought that the whole thing was good in general; there was a lot of action which made the book actually interesting. I also really liked the relationship between Cammie and Zach in the end, I think that they had developed well and that the relationship was a relatively healthy one, as she was not completely dependent on him. I mean, she wasn't dependent at all? She kept wanting to know where he was, but that seemed mainly because she cared There is a difference and I think that this book showed it well. 
 Zach himself was kind of annoying. Like, okay, you were raised in the Blackthorne Academy where they Teach Torture, and you were raised with the Crazy Circle mother, but please shut the fuck up for a while with the whiny emo, staring into the middle distance, "Maybe I am meant to be one of the bad guys," and "Maybe I am the bad guy," shit. That is SHIT! Cammie spent the summer with the circle, and she still didn't know what happened to her! In the last book, it seemed like the Circle had programmed her to be evil and kill people, and to jump off a building, and to do shit! They could have got her to do anything! Cammie (even though she is still an annoying bitch) didn't whine like that, so Zach just needed to calm down! 
 I thought that the entire thing with Bex was unbelievable: (view spoiler)[Okay, she was shot pretty damn badly, as there was an entrance and exit wound. They are spies with medical training in a dire situation and they were saying that she should be going to the hospital, which just shows how bad the wound is, in my opinion. There is no way in hell that Bex would be up and ready to go in the time she was without proper medical care, especially with enough energy to sneak into the room and stand there against the door in an ~oh so cool~ way... whilst they were arguing about her going to a hospital. And then you never hear of the injury again! (hide spoiler)] 
 Also, another unbelieveable, but extremely predictable thing (this is YA lit at the oldest): (view spoiler)[ For an extremely difficult and dangerous operation, nobody died. Not one of the main characters, or the secondary characters died, or were even severely and permanently impaired by injuries caused by this. It is impossible, but it happened. Of course, there was Cammie's father, but that was actually before the books began, so it doesn't really count. Obviously this is what I was expecting, and I am not very disappointed that this happened, really, because it was expected. I just kind of want to go and read the second book in Game of Thrones, where everybody is in actual and real danger. I think that this immunity against death also stops me from getting completely into books; when the main characters cannot die, it means that nothing that bad can happen to them, so I don't care so much. (hide spoiler)] But that goes for a lot of books, not just this series. 
 Finally, as I was saying to my friend once I finished these books; I really think that they would have been so much better if they were aimed at an Adult audience as opposed to a Young Adult or even Child audience. Plus, if the girls could have been a tiny bit older. There are so many things that Adult books can do to make it seem more... spy like and dangerous that you cannot do in books aimed for a younger audience, and I really love this idea. I would love to read a series like this but more explicit in the action, but I have not seen one.