I really liked most of this - I was invested in the story for the most part and it was gripping (particularly the beginning) and made me not want to put the book down. I liked the way in which Kowal used an alternate history to tell the stories of groups of people whose contributions have systematically been down-played in history. Sometimes, I felt that the obvious pointing out of racist and sexist biases at all points intruded on the story, and I would have rather that this was done in more showing way rather than just straight telling like 'wow, I can't believe that there aren't any black people on this list' (paraphrasing here) over and over again. But I appreciate the importance of getting these biases across to the purpose of the book. 

I didn't particularly like how choppy the story felt in parts and some of it felt like it wasn't really serving any purpose by being in there. The repeated puns/jokes/double entendres were grating and sometimes stretching quite a lot to get there. I also find it highly unlikely that a maths genius and her rocket scientist husband, both of whom work in rocketry, would make a bunch of dirty jokes that stretch technical aspects of their field so much to be inaccurate. If anything (and this is taken from my own interactions with people in various specialisations - including myself), jokes in your main technical field of expertise are hyper-specific and generally only funny to others who have the same technical expertise. So I find it quite unrealistic and inconsistent with their characters when Nathaniel and Elma are making a bunch of jokes about turning the key in each others' ignitions and handling rockets. This was the same with the maths, with some particularly stretched jokes about prime numbers. I had other minor gripes with a lot of the other banter between Nathaniel and Elma as well and found I was really just trying to push through those parts to get to the more enjoyable parts of the story.

The issues I had with the book were minor though, and I felt compelled to keep reading right through to the end. Definitely a great read if you have any interest in alternate histories and space exploration.