An excellent second installment in an ambitious, creative series. 4/5. 
 This review was originally posted on my book blog. 
 This is a difficult book to review without including spoilers for book 1 of the series, the terrific Illuminae. If you'd like to know about that, please read 
 my review here 
 . The short version is that I only gave five books 5 stars in 2015, and Illuminae was one of them. 
 Though I can't say much, I'm delighted to say I enjoyed Gemina almost as much as book 1. 
 I didn't warm to the new set of characters we meet in this book as much as those in book 1, but they're still an engaging bunch and you care about them enough to keep turning the pages to see if they'll survive. 
 This is one reason why I've rated the book slightly lower than book 1. The other reason is that the formatting, which I felt was only occasionally irritating in book 1, goes further in book 2 and actually impeded my ability to read the story several times. I'm all for originality in storytelling and formatting, but I don't want to be yanked out of immersion in the story because I'm having to turn the book round in circles or get out a magnifying glass to read the text. 
 I have to give the authors points for their skillful handling of a plot which is complex in the first two-thirds of the book before becoming truly mind-bending in the final third. 
 Overall: not quite as thrilling or gripping as book 1, but still very good. I can't wait to see what Kaufman and Kristoff come up with for book 3!