This was very well-written, but offered no original insight into its subject. The author is clearly an Establishment figure (I laughed aloud at his sniffy, purse-lipped description of the new millennium party at the Millennium Dome) who had no desire to discuss the Queen Mother in any depth for fear of upsetting her relatives, who had cooperated with him in the writing of this hagiography.
For example, we learn that she took many months to consider Bertie's proposal, but there was no mention of the common belief that, encouraged by her social-climber of a mother, she was actually holding out for the bigger and more handsome prize; his older brother, the Prince of Wales. This was certainly Wallis Simpson's opinion, and it was shared by several 1920s/1930s Society figures - why was it not explored?
The deaths of Princesses Margaret and Diana merit a page or two apiece, yet the QM's safari, and her trip to Canada, are dealt with in excrutiating detail. I skim-read several sections of this book.
In short, if you want to know exactly what the QM was up to on 1st June 1936 (or any other date), this is the book for you. If you want an analysis of her motivations, character and beliefs, then look elsewhere.