I loved the idea behind the sentinels and the tree tattoo that visually displayed how long until they had to find their mate before they lost their soul. The only exception is, that I would have liked it better if they were fated couples rather than a possibility of multiple matches. I thought this reduced the significance of the mating especially when it stands to reason that the male would be desperate for pretty much anyone compatible with him. 
 All the characters were really engaging. I don't really like a lot of subplots and this book wasn't an exception. I find that when this happens it takes away from the main storyline a little. In the end, the subplot characters usually end up with more storyline by the time they get their own book. However, I'm glad to see that I recognize a few characters in the next couple of books.