The Moral Landscape is Sam Harris' explanation of why science has useful and relevant things to say about morality. I tend to agree with this position, so it is hard to separate myself and imagine what this book would be like to someone who believes that morality can only come from religion.
It is important to note that Harris defines "science" in this context not as what men in white lab coats do, but in general as scientific thought applied to all kinds of fields including biology, psychology, economics... all that. His claim is that even if we don't always know how to maximize happiness and minimize suffering, there are scientific ways to look at it and these are more valid than a morality based on dogma alone.
Another important note is that Harris' is not claiming science can, at this time, definitively answer all the questions of this nature. We may eventually get there, or not. The important thing is that we try, and try to base our morality on what we know to be true about the world.
I feel like I explained this poorly. I guess an example might be contraceptives. Some people base their views on contraceptives on the pope's stance, or their church's stance, or what they assume to be the bible's stance. Others may base their views on human happiness and suffering. These different bases might lead to very different opinions regarding condom distribution and education in Africa, say. Whether or not condom use is punished after death, it seems clear that more and better condom use in Africa could reduce human suffering here on planet earth.
Harris fleshes out The Moral Landscape with examples and bits of evidence from various fields of research as diverse as brain scanning and psychological tests of animals. Some of these examples are the most interesting parts of the book in my opinion.
I think this is a very useful and interesting book. I would recommend it to anyone at all interested in morality or ethics, and I would be very interested to hear what people who disagreed with the book's premise thought about it.