I read this one as a companion piece to Haidt's _Righteous Mind_-- both were recommended to me by the same person, and they are of a piece. Appiah even quotes extensively from the research that will form the basis of Haidt's book (though this book is published a few years before Haidt's, it seems the foundation of Haidt's book, and his research, was published before this one. That confused me for a bit, so I wanted to make a note of what I think I figured out here). Where Haidt is interested in "moral psychology," understanding what people do, Appiah, as a philosopher of ethics, wants to think about how to get people to do good.
And really, the book is a pretty solid and brisk survey of a lot of philosophy over time- you get Aristotle, Mills, Kant, and many others, all of whom are connected to this ideal of how we know what is the right thing to do and how we can get people to achieve the good. Appiah has an interesting approach-- partly, he reads like a popularizer, so you feel a bit like you're getting these tracts of summary that are helpful for a noob, but maybe not totally necessary to "real" philosophers. But then, he'll drop in some insightful riposte and you wonder, oh, maybe he's totally reconfiguring these guys and this is part of his method, and it's for "real" philosophers. It's a lame excuse, I know, but I might not have followed the whole book, because I am that noob.
The basic premise is that a) philosophy has a bit of a disciplinary problem. What we call philosophy used to have a much more rounded approach-- experimental as much as mental. And b) if we reintegrate some of that experimental method, even if that just means reading research in cognitive psych, etc, philosophers can heal their field and lead their thinking forward, at least some. But Appiah never quite gives the knockout punch, where philosophers went wrong in their imagining about human nature that the new science has exposed. (In fact, on occasion, it's when early philosophers who did science talk about humors, etc, that we think they are silly.) Appiah makes some interesting points, but for me at least, they remained kind of academic, limited to the way the discipline conducts itself, and didn't necessarily change my thinking.
One thing I think I did learn, though, is the difference between English types (me) and philosophers: I don't think most literary folks care about the race as a whole, or the average person, or the human experience in general. We are, I think, much more interested in the particular-- so when I read Appiah, pace Aristotle, talk about increasing the state of eudaimonia, I wonder, in so many words, who cares. I care a lot when it's David Copperfield or Jane Eyre, but the rest of the people-- forget about them. Appiah makes me think maybe philosophers do care about those people! Crazy, man.