I picked this up based on reviews I've read about an earlier edition. As a relatively new dungeon master who is about to launch my own 4th Edition campaign I thought this book could be helpful.
To be positive, the book was helpful in a lot of places. However there were a number of places, such as the section where the book discusses creating adventures, where I felt the book could have gone into more detail.
However what turned me off this book was the constant advertising spam the authors inserted for other WOTC D&D products. This annoyed me for three reasons. Firstly, a lot of the promotions were out of context with regards the material being discussed. Secondly, at times they interrupted the flow of the topic the authors were writing about and lastly they pushed the same product over and over again.
All in all the book contains some good advice, but it is overshadowed by a large amount of unnecessary advertising.