What I liked: First, I liked Immune but it wasn't as compelling as the the first book. That's not to say I didn't like it, actually I felt it was more of a transitional book and I read it extremely fast.
Ms Mayer is still establishing her characters and building her world in Immune. More so than in book one. I'm still learning how to connect with Rylee. She has good traits and bad. She jumps into most situations without a plan or based strictly on her "gut reaction". It some cases it's understandable but in others, I wanted to smack some sense into her. That's the thing, I get why and what she's doing but quick risky decisions have me shaking my head.
Now, O'Shea is a different matter altogether. I love his character and am really looking forward to what Ms Mayer has in store for him. He could be Rylee's voice of reason, if she will let him. There's some tension between them in a romantic sense that I really wasn't expecting based on the first book.
The action is non-stop and the trouble just keeps coming. The characters flow from one crisis to the next. My very favorite thing about what Ms Mayer is doing with this series is the way she provides the reader with the character connections. The first time a character is mentioned in Immune, it's linked to a profile on how that character relates to Rylee and some background on the character. You "click" on it and there the information is to refresh your memory. Hit the back button and resume the story. This is the very first series I've ever seen this done. When a reader is dealing with a group of characters, this innovation clarifies each and every character to refresh your memory.
What I didn't like: As mentioned, Immune wasn't as gripping to me as the first book but it did move the story along and there is no lack of action.
I'm currently reading book five in this series. I've read them one right after the other. I can't get enough!