Fairly satisfying end to the series, still focusing on the ethics of the situations more than little things like action, but that's fine because the tension is all right there for us. The reveals really came to a nice head in this one, with serious choices needing to be made, and it really isn't all about the nuke in the background or even in the foreground. 
 It's about whether either species should continue to live, whether all the species could be considered one, or, as everyone else seems to think, we should all go to hell in mutually-assured destruction. 
 This *could* be considered an old YA theme, and you'd be right, but this one doesn't pull the punches or shirk from asking the hard questions. It focuses on exactly that and hones away at it. 
 I like that. At least for me, these questions more than any of the plot or the relationship stuff made the novel something very good. Personal preference. :)