This book had some really fun and interesting ideas - the characters' backgrounds, military corruption, the whole creepy theme of nostalgia being deadly and the physical ways that nostalgia manifests - but none of it was anywhere near developed enough. It felt as though it needed to be twice as long, which is odd since it's already 460 odd pages. But I constantly felt like I wanted more, because what I was given never felt like enough for me to be fully immersed and engaged. 
The story also felt rushed at times, particularly at the beginning, which made it very hard to grasp what was actually happening and follow along. I think the idea behind the main plot is complex enough that it needs a lot more exploration.
The two main characters were lovable, as was their dynamic. I think that the time given to exploring the depths of their personalities was enough for them to feel like fully developed characters, but I still think that there should have been more; they both have such interesting backgrounds that it seemed a pity to not spend more time on them. Their relationship and it's development definitely needed something more, too - when we meet them, they already have an established dynamic, and it remains somewhat stagnant until near the end of the book. 
All in all, it was an okay read - definitely fun, but tempered by frustration.