Cytonic was a pretty good penultimate book for this series. 
I did like the adventure aspect of the book, although it could feel a bit unfocused sometimes. I loved the stuff with the pirates and Surehold-it was fun and showed another aspect of the Superiority. I also liked Chet and his journey with Spensa throughout the book.

I've seen this book get flak for not including the Skyward Flight characters and instead setting up a new cast, but that wasn't that much of a problem for me, perhaps because I had read the first 2 Skyward Flight novellas before this and I had already read about what was going on with them, so I wasn't noticing their absence THAT much.

In any of my Sanderson reviews, I have to talk about the final act because he is just so good at writing it. This book had an absolute banger of a  Sanderlanche.

As for criticism, I feel like at some moments Spensa sounded a bit too mature, if that makes any sense?  Also, as I mentioned earlier, some of the adventuring was a bit unfocused and maybe could have been trimmed down. Overall though, this was a solid book. I don't understand why this receives so much criticism-I personally enjoyed it.

Edit/Addition: I've just realised there was not a lot of important stuff that happened in this book, and while most of the book might come across as filler to some, I think I was invested enough in the character arcs for that to not be a problem for me.