I had looked at a couple of other books on Bayesian statistics and noticed that they all focus mainly on all kind of very technical aspects. Sivia's book on the other hand deals almost exclusively with basic applications of Bayes theorem. It does this by discussing a number of examples in detail. This makes it much more useful people like me (I am a physical chemist), as I can often simply copy what Sivia does. I rarely feel the need to consult the more advanced books.
In the second edition of the book a chapter on nested sampling has been added written by John Skilling. I have seen that this technique can be very useful, but only because I found a paper in which it was described much better than in the book. It is not just that a completely different notation is used by Skilling, also the whole approach is different. Whereas Sivia aims to write an introductory textbook, Skilling seems to write for specialists. This really lessens the quality of the book.