Epstein has what he calls a classical liberal reading of the Constitution. His argument is that as the bare text itself cannot yield determinative answers to hard cases, what is needed is to understand and isolate the theory that animates the text.
(In that formulation, Epstein rejects out of hand Scalian Originalism, which, he contends, has nowhere ever been functional in constitutional interpretation.)
Epstein argues that that theory is classical Liberalism that limits government, vaunts private property, protection of individual rights, freedom of contract, and most fundamentally personal autonomy. Hard cases fall to be decided on principles that are consistent with and enhance that animating theory.
Sunstein's basic criticism of Epstein is that his, ultimately, is an arbitrary moral imposition of his own present preferred views, which views are not supported by an exhaustive historical demonstration of their informing the constitutional text. Others take different views of what underlies it.
My own thought as to what Sunstein argues is to wonder whether he agrees with Epstein's fundamental proposition that as the bare text yields no determinative answer what is needed is the theory that animates the text and by which hard cases fall to be decided.
If he doesn't agree, what is his principled account of the resolution of hard cases? If he does, what theory or theories does he postulate? http://www.newrepublic.com/article/117619/classical-liberal-constitution-richard-epstein-reviewed
For as much as I enjoyed Sunstein's lucid and highly accessible review of Epstein's thinking and his book, the meal would have been even more satisfying had Sunstein touched on his own thinking on these issues.