My first comment is not really on topic, but it really astounds me that the people who make the covers for these books don't even make an attempt to have them suit the book. This one is hands down one of the worst in terms of matching the theme or events of the story. I just don't get it at all. Anyway... 
 This is my first steampunk in a long time and I really did enjoy the story. The nanobots was a cool addition to the more usual steampunk thing. I loved the alternate history aspect and the Mongolian Horde as the "evil empire." Overall, lots of really good things happening in the book. 
 Rhys was not my favorite hero ever, not by a long shot. I say this as a wildly outspoken supporter of alpha males everywhere: he was overbearing to the point of being an asshole. Now, his asshole tendencies did fit his character quite well. The problem was you had to get 60% of the way through the book to see why he was that way and for people who don't like their heroes really obnoxious, I think that's a tough sell. That said, his behavior was character and world appropriate. I know there are a lot of people who found him a bit too rapey, but I didn't feel that way. He is very, very alpha and I'll leave it at that. 
 Mina was great. She had a nice combination of strength and vulnerability. The perfect amount of damage in a main character. I did think her about face was too abrupt. She went from being scared and mad at Rhys about something he did (which I won't divulge because it would be a pretty big spoiler) to just about jumping his bones within a couple of pages. I just didn't buy that. 
 Anyway, a must read for steampunk fans and I think it would work for most anyone with a Paranormal Romance inclination as well.