It was good as always. I am a huge fan of Rachel Caine and I read all of her series and liked them all. Her books are always interesting, with great characters and a lot of action. And "Unseen" is not exception to this. 
 I find Cassiel an excellent character. She is unusual and memorable in this huge amount of urban fantasy lead heroines. And what I think is making her distinctive is the way she thinks. Other characters often use "cold" to describe Cassiel. But she is not. She is just very logical, pragmatic and calm (she is totally opposite to Joanne in Weather Warden series, who is impulsive and all her action came from her fillings). 
 In "Unseen" we finally get to see a development in Cassiel and Luis relationship. I like Luis, but sometimes I get this feeling, that Cass is stronger than he is. And not in physical sense but in mental one. She is always the one who made tough decisions and have to deal with the consequences of it. 
 The problem that I had with this book is the mortality level in it. It is the third book in series and in every one of them people keep dropping off like flies. Only we get introduced a new character, BAM, he is dead. In Weather Warden series a lot of people died to, but it can't compare with mortality in Outcast Season. Ms. Caine, please, stop killing so much of your characters (especially children)! 
 I really hoped that we get to see main characters from Weather Warden. I miss Joanne, David and Lewis. But the events in "Unseen" occurred in time of Warden sea travel, so we don't get to see any of them. I just hope that there will be crossovers in the next books. 
 Conclusion: the quality of Outcast Season is the same. And in Russian we had this saying that "Constancy is the sign of great talent".