I'm sad to write that I was disappointed with Unseen. It lacked the excitement and adventure of the first two books. The attraction between Luis and Cassiel was missing; they almost seemed to be going through the motions. I was extremely annoyed with Luis's reaction to the task that Cassiel had assigned herself. He didn't have to like it or agree with her, but he should have supported her decision. It's not like he didn't know the reason she was placed on earth as a human. The last fifty pages were interesting but it didn't make up for the rest of the story.
I read the Weather Warden series before beginning the Outcast Season books and what I've noticed is that in Caine's story arc, there's always one book where the characters are at odds for a prolonged period and their separation is painful. Painful for both the characters and the reader. It's the price you pay for the heightened intensity of the storyline and the dangers faced. So since the series is only 4 books long (so far, I have hope :), this one is that book. And you know what? I'm fine with it - tons of stuff happen, it's very exciting, and the story moves through physical and emotional obstacles like the Hulk! You need this book in order to understand what happens next. I can't wait!