Tula! It's so much worse knowing what happened to her... yes its not explained in full detail (thank god) but what is explained leaves little to be desired. Yelena is still a strong character, but she has more speed bumps in this last and concluding novel. She tries to push everybody away, as she is afraid of hurting them while hurting them in the process. A silly, but classic maneuver from what I've read. Snyder does a good job of it, by not making it too blatant or annoying. 
 I liked (but did not enjoy) her devastation over thinking that Valek was dead, as it truly showed how much she cared for him. And I'm happy with how everything ends up neat and tidy. Well, if you count going into the fire dimension and siphoning a nasty piece of works soul into a glass, then yes, neat and tidy. I hope the few lose threads are mentioned in the second series.