What had stuck in my mind when I'd read of his work some years back was his idea of "second order desires", wanting to have the desire for X even if you don't have the desire for X (e.g. for healthy food), and how having these second order desires can be seen as a form of free will--without second order desires, you are simply driven by your first order desires (like an animal).
Just googled it for a refresher and found this[1] comprehensive but readable explanation of the above idea. The obituary refers to it briefly as well.