I liked Wither, but it wasn't my favorite. The sequel really impressed me. As Rhine's world widened I was able to see more and more what the world had come to in this dystopian future. Instead of being just a filler book I feel like Fever upped the stakes in the trilogy. The only thing that I would say it suffered from is how she kept moving locations. I wasn't able to really get a feel for the settings in a way that allowed little details to make an impact like I was with the first. The escape feel is pretty typical of a dystopian sequel but I think it makes it difficult to really reach out to the reader.
Rant mode: Once again I like the wrong guy! Linden, despite being an airhead, is so much more interesting then Gabriel. I hate to use the movie terms but Rhine and Gabriel have zero chemistry. He just feels like super-boyfriend while Lindon at least has good/skeezy moments.
I can't wait to see how this turns out!