This book offers a great deal if you are interested in the history of ethics; particularly, what the great philosophers had to say regarding ethics, and what movements have re-shaped ethical discussion (e.g. romanticism, the reformation etc).
MacIntyre displays a thorough knowledge of the ideas of the ancient greek philosophers, dedicating a large share of this book to Aristotle and Plato. His outline here is very impressive, which addresses the complexities in understanding the subtle differences in meanings in greek language, and how these differences can help us understand the mindset of the people and the times (for example, the equivalent words for terms such as 'good' connotated slightly different things, e.g. one could not be 'good' and fail. For in some cases, 'Failure' was a closer binary opposite to 'good' than many terms which would seem more meaningful opposites today).
Unfortuneatley, the section regarding christian ethics is very slight (particularly early, through to the medieval period), which leaves this an unbalanced work, considering there is three whole chapters on Plato. He confesses that his understanding of christian ethics was inadequate at the time of writing thsi book, and highlights errors and inadequacies in the preface. For this reason, I recommend buying this routledge classics edition, as it has a superb and honest preface, where MacIntyre expresses how the book was recieved and acknowledges a number of criticisms.
The book is noteably impressive for the outline of greek ethics (and contextualising them), but there is a very good account of the key approaches to ethics in the 1600s, 1700s and 1800s, e.g. regarding Kant, Hegel, Marx, Nietzche through to the movements of the 1900s (e.g. utilitarianism) and then onto early 20th century writers (Ayer, Warnock and Satre among many others).
The book is challenging to read in places but always rewarding. Its weaknesses are made up for by the fact that he acknowledges them in the preface, so you are aware of these weaknesses as you work your way through the text. A great work, well worth reading.