This book, this book! 
 I picked it because of the gorgeous cover and had no expectations. It started slowly, with an initial burst of action promptly interrupted by some lengthy infodump-heavy flashbacks. They cropped up now and again throughout the book, sometimes awkwardly, and are the main reason it didn't get five stars. Once the story got rolling, though, I never looked back. 
 The book is part sci-fi adventure, part romance with - yes, sorry - the obligatory love triangle. I know some other reviews complained the romance dominated the plot but I found the balance worked well, and while the romance may not have been the most original, it was beautifully written and swept me along, especially the sections taking place in Imperial Russia (!). I could have spent a whole book in that world with those versions of the characters. 
 The sci-fi plot had enough mystery from the early pages to keep me intrigued, and enough action to keep the story moving. Some of the plot twists weren't much of a surprise, but it didn't spoil the story or feel like an anticlimax the way it sometimes can. 
 There's no denying it's a very character-driven book. Personally, I like that and I loved the book. However, if you're after something that's action and incident packed without much attention given to the impacts on the characters and their relationship (not just the romance, there's a fair amount of focus on family, too), this may not be the book for you.