Parfit's Mountain

At Brian Leiter's blog, the discussion of Simon Blackburn's scathing review of On What Matters (Derek Parfit's opus magnum) continues.  Here's a review by Jussi Suikkanen in the current issue of The Philosopher's Magazine.  He makes an interesting and very fundamental criticism of the book--

What strikes me most now is the philosophical method which Parfit employs again and again throughout the book. It is the oldest tool in the philosophers’ kit. Parfit proceeds by attacking familiar versions of general ethical principles with innovative counterexamples. He then makes these principles more and more sophisticated until they survive the thought-experiments.

....  Unfortunately, Parfit applies his method also when he takes part in the debates about the nature of reasons, rationality, and free will, and especially in the metaethical debates about the nature of normative thought, language, properties, and knowledge. Perhaps because of this, Parfit’s work is less successful in these areas outside normative ethics. This shows that, as an area of intellectual investigation, metaethics differs from normative ethics in significant respects.

Metaethicists attempt to construct broad illuminative accounts about our practical engagement with the world by trying to combine elements of philosophy of mind and language, epistemology, metaphysics, ethics, and even psychology into all-encompassing, coherent, theoretical wholes. Even if there are always of course details to be given and technical problems to be solved, metaethicists try to build big pictures with explanatory power. Such theorising does not proceed by formulating succinct principles and testing them with counterexamples.

That seems right -- if so, it's a devastating objection.

I'd like some honest soul to give me a frank appraisal of the book's readability.  A chore or a delight?  The reviews I've read so far--Singer, Blackburn, Suikkanen--don't say.