I found this to be an excellent reading and also somewhat unique from the perspective of a German scholar for a change (and not an anglo-saxon one). The author is very methodical and quite organized and he himself admits this is a serious feat. At times you will find that it's not entirely up to date, as he mentions meeting people during the early 20th century. I can well imagine that some things he talks about have changed or our understanding of these changed to some extent. Totally recommend for those who are interested in world religions.
It provides a profound explanation for all five world-religions. However it's extremely dry, pretty hard to get through, maybe because of the need to make it as compact as possible to make is monetarily accessible for people from all backgrounds, as stated in the introduction. Overall very useful for open minded people who want to understand all viewpoints of a religion.