Like most works by Schaeffer A Christian Manifesto contains Schaeffer's standard rundown of Western Civilization after the Reformation. If you've read any of his books you probably know his take on things. However, the reason I would recommend this book is his emphasis on how Christian truth is not just for Sunday mornings. It affects every facet of our lives, including politics; which, prior to the 80's was a field that most Evangelicals had previously been reluctant to enter. His insight into the acceptance of abortion in Western culture is unique and must be read by anyone who wants to understand the issue.
With these good points, I must point out that some of his historical analysis, with regard to the Reformation, is definitely faulty. He tries to point out how political activism of the Reformers insured the success of the Reformation in Northern European nations. Then he tries to tie it to peaceful (to an extent) anti-abortion activism. His historical analysis is so scant because he probably wouldn't want to point out that the reason the Reformation was successful in those countries because the reformers themselves promised a select group of nobles absolute power and free reign to loot Catholic lands. Once the rulers were in the hands of the reformers they could enforce whatever they wanted to.
Despite flaws like this felt that overall it was a good, thought provoking read.