Most introductions to Existentialism make either of a couple of mistakes: they either focus on the style rather than the substance of the thinkers subsumed under the label or they focus on the mood evoked. Anyone who has read much about the philosophy knows that it is all too easy to degenerate into a meditation on the angst of human existence. By centering their discussions on moods and attitudes rather than concrete philosophical positions, Existentialism as it emerges from far too many introductions become anything and everything, yet nothing at all. Not so with Flynn.
The book is broken into six (necessarily) short chapters. The first five justify the cost of the book. The last one, on "Existentialism in the 21st Century," is an unhappy addendum. It seeks to hint at ways that Existential thought can engage some of the ongoing philosophical debates that continue into the 21st century. But the various ideas are simply dealt with too briefly and the possibilities of engagement are more gestured at than explained. The intentions were good, but there simply wasn't enough room to produce more than an outline of a chapter. But the first five chapters are all lucid and sharply focused. The first chapter deals with the central tenet of all thinkers who can be considered Existentialists (it is important to remember that most "Existentialists" did not so consider themselves), that philosophy is a practical discipline, dealing with actual lived life, not an inhuman scienticity far removed from concrete human concerns. The second deals with what it means to become an individual and how that is achieved. The third begins with Sartre's famous lecture on humanism and uses this as a springboard to talk of both theistic and atheistic forms of existential thought, but showing how both nonetheless place human beings at the center. The fourth chapter delves into the important ethical concept of authenticity. Finally, the fifth chapter deals with an aspect of Existentialism that many books on it neglect, the social philosophy promulgated by many of the movement's leading thinkers.
Not all those considered Existentialists receive equal attention in this intro. There is a great deal more about Kierkegaard and Sartre than any other thinkers, though there are significant discussions of a host of additional philosophers including Merleau-Ponty, Camus, Heidegger, Nietzsche, de Beauvoir, and Marcel. I have read fairly widely in all of those thinkers except Merleau-Ponty and can attest that his discussions of all these individuals are consistently accurate and fair. I admire how clearly he is able to get to the crux of their central ideas without distorting their thought. I'm especially conversant with Kierkegaard and while I often would have like to seen certain points expanded, I cannot say that he says anything misleading.
I recommend this as an introduction to Existentialism over all other such books with which I am familiar. Though still of value, some of the older intros by people like Walter Kaufman and William Barrett are definitely showing their age. They also suffer from the disadvantage of having been written while Existentialism was still in its hey day and they had less of a sense of what would be deemed of ongoing value in the movement. Flynn has the advantage of hindsight and knowledge of what parts retain interest. I have read several outstanding entries in this series by Oxford and feel that this is one of the best volumes yet.