As usual, Harris offers more rhetorical posturing than substance. His position is utilitarianism guised as science and, as a result, many people will unfortunately be inclined to see what he's doing as new, and will agree with him.
Kwame Anthony Appiah, writing in the New York Times, has some very different things to say about this book:
"In fact, what he ends up endorsing is something very like utilitarianism, a philosophical position that is now more than two centuries old, and that faces a battery of familiar problems. Even if you accept the basic premise, how do you compare the well-being of different people? Should we aim to increase average well-being (which would mean that a world consisting of one bliss case is better than one with a billion just slightly less blissful people)? Or should we go for a cumulative total of well-being (which might favor a world with zillions of people whose lives are just barely worth living)? If the mental states of conscious beings are what matter, what's wrong with killing someone in his sleep? How should we weigh present well-being against future well-being?"
"It's not that Harris is unaware of these questions, exactly. He refers to the work of Derek Parfit, who has done more than any philosopher alive to explore such difficulties. But having acknowledged some of these complications, he is inclined to push them aside and continue down his path."
And in conclusion:
"Yet such science is best appreciated with a sense of what we can and cannot expect from it, and a real contribution to the old project of a "naturalized ethics" would have required a fuller engagement with its contradictions and complications. Instead, the landscape that the book calls to mind is that of a city a few days after a snowstorm. A marvelously clear avenue stretches before us, but the looming banks to either side betray how much has been unceremoniously swept aside."