I agree with a previous reviewer in that out of all the books I have come across on Optimal Estimation, this is by far the most suitable for self-study. I have found his explanations to be concise and straight-forward. That is, he goes straight to the point and delivers the concepts using simple/common language which is non-characteristic for academic books in the areas of Systems and Control. For a sample text on the subject written by him check his article on Kalman Filtering on the site embedded[dot]com
While conducting research as part of an Independent Study course, I have treasured this book like no other since it continuously serves as a valuable reference. The first two chapters which review the underlying mathematics (linear algebra and probability) necessary for understanding the central themes of the book are also above the usual presentation in related books. Needless to say that readers should not expect to learn the Math from this book alone, however, they can expect to find in these chapters most of the topics that usually need a quick review to make sense of higher-level concepts in the text.
I cannot stress enough that his use of language and clear explanations make this an easy-to-read textbook which simplifies the understanding of the topics. Do not get me wrong though, to really understand the problem of state estimation the readers need to be quite prepared in different areas of Engineering and Mathematics (hence my motivation for self-study).