I teach Excel on a regular basis. My students are all working people who need to be able to use Excel in their jobs. I teach at the beginning, intermediate and advanced levels. This book makes an excellent text, and each student gets a copy. For each topic I discuss in class, I give them directed reading in this book. It makes a great reference. In some other reviews, I have seen complaints that this book is very difficult to learn Excel from. I can see where that would be true; but, once you have a base of Excel knowledge, this book is very good for building further skills. It is not for the novice who has no other source of learning.
Excel is such a huge topic, that it is impossible to cover it all in one book. As with all other Excel authors, Walkenbach has omitted some things. The most glaring omission is the Subtotal command (not the function). I am continually amazed at the people who have been using Excel for years and don't know about this command. It is not covered in John's book (at least, I haven't been able to find it even with a PDF search), but the subject is covered pretty well in Help and is easy to find there. The other subject I wish he had included was Advanced Filtering. Advanced Filtering is a true workhorse in Excel. Any heavy user of Excel should know how to use it. I feel it is more valuable to the daily user than the intricacies of array formulas. If he had covered those two topics, I would have given him five stars. Regardless, this is a very good book.