The Blinding Knife is what a sequel should be. It takes the action and magic that made The Black Prism good and made it better while toning down a lot of the exposition and over-characterization that made it a bit of a drag at times.
On the plus side, the magic system has a lot more depth than it did in the first book while at the same time not spending quite as much time hitting us over the head with terms we don’t quite understand yet. Even if I don’t necessarily like some of the choices (like why you can’t draft green from white light by default), it’s still a well done system. Otherwise, the worldbuilding has gotten bigger. Magical trading cards. Seers. Old Gods.