This past week, I re-read Catalyst so I could write a review of it. It's a good book! Rogue One is one of my personal top-ranked Star Wars movies, so I loved getting to read a whole book that adds extra content that enriches it so much more (not that it needs it, of course). Learning more about the Ersos and their relationship with Krennic is really interesting, plus we get to learn more about the early days of the Empire and how the Death Star really came to be.
Spoilers ahead for Catalyst by James Luceno.
I think the highlight of this book for me was getting to know Lyra Erso. Though her appearance in Rogue One is very brief, she still shows a lot of strength and admirable bravery in it. Here, we learn even more about her background. Lyra is an expert with surveying new lands, and puts her skills to good use many times in the book, to help Galen's research and when they need to escape at the end from the Empire. I really liked learning more about her character, and enjoyed how she was the one through the book with the strength to resist Krennic's threats and was suspicious of the Empire's real plans through everything, even when Galen was too focused on the work he was doing. In Rogue One it can be easy to see Lyra as another brave but tossed aside mother character, so getting to learn about her being smart and capable and having a valuable skillset of her own was really, really cool.
This book also provided a lot of insight into Galen's character. He's extremely science and mathematically-focused, and it's really only Lyra (and baby Jyn) who are able to soften him. I think his arc in this book is really well-done. He is first extremely resistant to doing his work for any government, and is shown to be very principled. However, over the course of the book you can see how Krennic manipulates him from the sidelines, by putting him in positions where the work frustrates him and is way below his talents, getting his peers roped into work on the Death Star and tantalizing him with the kind of research he always wished he could do. Eventually, the man who didn't want to even want to think about governments or wars is so embroiled in work for one (though to be fair, Galen doesn't know his work is being weaponized, he thinks he's studying it for energy conservation) that he neglects his marriage and family. It's a really fascinating, subtle and realistic arc to go through as you read, and it just shows how manipulative Krennic can be.
I think something else I really appreciated about this book was the kind of worldbuilding that we got to see in it. The story takes us from the tail-end of the Clone Wars through the creation and early years of the Empire. We've seen those time periods in other Star Wars media, like in The Bad Batch especially, but we've don't really get to see this change from the civilian side of things as much. It's really interesting to see the perspective of characters like Galen and Lyra on the sudden end of the war and change in government, and how the Empire is covering things up to the common people of the galaxy. I really felt like I could understand what it would be like to be living in the galaxy from this book, and how the propaganda and fear tactics got people in line.