Defiant is the best novel in the series right next to Skyward. I thought the books took a bit of a dip during the middle two, but Brandon Sanderson brought it all together very neatly. Defiant not only serves as a solid conclusion for the series, but as an excellent jumping off point for the sequel series.

My one critique is that the twist with the villains isn't well set up. But since the main focus is the complexity of the characters going through their well plotted arcs, that didn't hurt the book too much for me.