I just finished this. His earlier and very funny recent book about Princess Margaret, "Ma'am Darling," is a Datalounge favorite, and I think this one about Elizabeth II will be too. Brown is a very funny satirist who wrote for Private Eye fro years, and he's obsessed with the Royal Family, and very funny on the subject.
The book is in some ways a very loose biography of her (and there's a fascinating timetable in it of what happened with the royal family on her last day of life), but it's best parts are about how crazy people tended to behave when she was around. Even people who confesses to be republicans tended to treat her with deference when they got to actually meet her, and those who professed top respect her usually made fools of themselves around her because they just more or less lost control of themselves.
Brown very clearly admires her, but he also seems to have no illusions that there was anything much interesting about her other than her incredible self-command. he also devotes a fascinating chapter to when she decided her horse -racing trainer Major Dick Hern was unfit for his job after he had a series of extremely serious health setbacks and treated him (through her flunkies) with surprising ruthlessness. As Brown points out, almost none of her other biographies talk about this incident since it puts the queen in such an unflattering light, even though it was the talk of the horse-racing world at the time. Brown thinks it shows how fallible we all can be to the worst side of our natures.
One thing that's interesting is how many surprising details he found about how others in the royal family saw the Queen from Prince Harry's memoir "Spare." Brown is (unsurprisingly, of course) that despite the level of detail in it, "Spare" is clearly ghost-written (and not just written with the aid of its co-author) because nothing in it sounds the least like Harry's actual voice.
Here's the Guardian review: