The Essential Guide gives a terrific overview over the 50 years of Doctor Who leading up to the anniversary special of 2013.
For me, who just got into Doctor Who over the summer, it was great to see how the show evolves from it's days as a black-and-white television show to the HD produced behemoth it is now. It's great to learn about the history of the Doctor and his foes and to have an overview over his companions.
However, it is just a general overview and it is also very friendly. I would have loved to learn more about the controversies and stories surrounding the show throughout the last 50 years. One sentence descriptions of the companions are just not enough.
But it definitely made me want to see the old, classic epsiodes and the pictures are fun to look at. All in all, it delivers exactly on its promise: it covers the essential knowledge and stories about the Doctor.