I sense the author is just pushing his own view on buddhism (or... existentialism) through this book: this is not a study of the crossroads between buddhism and existentialism, but the author's own view on buddhism expressed in the terms of existential thinking.
St. Batchelor in this book holds a view about buddhism very much close to that of contemporary Vietnamese zen buddhism. They see the world as manyfold manifestations all sprung from one unique universal 'tank' ('alaya vijnana'); consequently they hold the view that all things and beings in this universe are linked together in complete solidarity. This is one view: but this is not really essential either to buddhism or to existentialism. It also seems to me somewhat oversimplified as a moral and as a cosmic hypothesis. Personal responsability and gratuitous compassion are closer to ancient, theravada buddhism.
Anyway, I much preferred--and would recommend--the same author's "Buddhism without belief" as a contemporary, 'modernist' approach to the ageless and visionary wisdom of buddhism!
If you are familiar with existentialism and buddhism, and you would like to read about their relationship, this book is great. But I would not recommend one to read this book for an introduction to either Buddhism or existentialism. For an introduction to Buddhism, I recommend Bachelor's other book, "Buddhism Without Beliefs: A Contempory Guide to Awakening". To learn more about existentialism, I would recommend reading the philosophy of Albert Camus.