This is a handy book if you want a brief summary of the world's major religions. Some of the facts and figures may be outdated, but the information isn't: it contains an explanation of each religion's origin, teachings, major figures and historical significance, as well as excerpts from its own holy book / creed.
I especially loved Heydt's introduction - it's worth it just for that. He makes some excellent points about monotheism vs. polytheism, and his Christian perspective is refreshing (non-Christians may not appreciate the introduction quite so much, but the remainder of the book is neutral).
The drawback for me was the layout. It would've been better to dedicate a chapter to each religion instead of treating them by subject. As it is, you read of all the different religious figures in one chapter and then all the different religious teachings in another, then the excerpts from the holy books separately, etc., so that I was constantly flicking between chapters to figure out which were related (and remember what on earth Zoroastrianism is!).
Otherwise, a good little reference to refresh your understanding of dominant world religions.