I just finished this book and gave it average (unusual for me when it comes to an Una McCormack novel--usually I really enjoy her books).
It took me a long time to finish it. Part of that is because I have some personal stuff going on. But there were times I didn't feel a great need to go back to it. Now, to be clear, I haven't seen season 3 yet (waiting to get the Blu-Ray since I don't stream), but I gather this novel is sort of a prequel to season 3 and sets up things for Burnham for where she will be there. While I knew she had jumped to the 32nd century, there were some things I was unaware of like the 'Burn' and the apparent fall of the Federation (though that's a bit vague--on purpose I imagine).
The things I liked about the book include the character development, not surprising as one of McCormack's strengths as a writer always seemed to be character development. I felt I knew Sahil, Book, Pa'Dar, and others pretty well in the book. Another positive about the book is it was written in such a way that I felt like she set things up well for when I do watch season 3, yet I don't feel like she gave away any major spoilers that will ruin season 3 for someone who has not seen it yet. Except maybe for the 'Burn.' But there was no way around that since it basically eliminated warp drive (and I imagine season 3 brings that up pretty quickly so it's hardly a big giveaway regardless). But there are hints of something more going on with a lot of that. I got the sense the show will address the cause of the Burn, if there is a way to undo it, and the current status, if any, of the Federation, and if it could indeed come back. The book hints at some of that without giving anything away, so that gave me some clues that will come up in season 3. I was curious about how the ships were travelling around without apparent warp drive (or did they have limited warp). I was never clear in the novel, other than the transwarp tunnels, how they travelled so quick. I would think impulse drive only would take years to get from one system to another.
So what dragged the book down for me. I hate to say this but at times it was a slog. There were a couple storylines going on, which doesn't always hurt. I enjoyed Greg Cox' A Choice of Catastrophes which had 3 major story lines but they were well balanced and each interesting in their own right. But with Wonderlands, there were some story threads I liked, and some that just weren't very interesting. There were some chapters I got through pretty quickly, and one or two that actually took me 2 or 3 weeks to get through.
So not a bad book, but not great. But still, I think it'll help build on season 3 so I'd still recommend it to fans of the show who want more on how Burnham adapted to her new circumstances and what is going on.