Besides offering a clear and nonvoluntarist account of Kantian freedom, Brandom strongly puts forward the idea that the formation of unities of apperception is an ethical task for Kant. This was new to me when I encountered it in Reason in Philosophy, and very exciting. Kant suddenly made a whole lot more sense, and began to look much less unattractive.
I have not had the opportunity to confirm whether this is just what Kant should have said by Brandom’s reconstruction, or whether he actually did say it somewhere. (In my early readings uninformed by secondary literature, I had taken Kant to be asserting that the synthesis of unities of apperception was something that just necessarily happened for any subject, qua subject. This seemed like an unattractive, failed attempt to establish objectivity on a subjectivist foundation.)
Secondary literature on Kant is vast, and much of it is outstanding in quality. Leading interpreters have deep differences, and this is as it should be. A mark of great philosophy is that it encourages creativity and spawns ever new interpretations.
If I could hazard a generalization, though, it seems that subjectivist readings of Kant are more and more challenged these days. To mention but one example, Frederick Beiser’s recent history of German idealism before Hegel is entitled German Idealism: The Struggle Against Subjectivism. Young Karl Marx’s 1844 essay on Hegel’s Phenomenology, which reduced Hegel (and arguably Kant as well) to a bad subjectivist cartoon of Fichte, is profoundly misleading. (See also Copernican.)