Right at the beginning let me say that I don't understand the constant harping on that this book somehow is a response/companion to/answer to/ response to/ argument against etc. to Said's Orientalism - A book I have tried and failed to read in it's entirety but recognize it as a much more serious, ground breaking, challenging, but definitely 'academic' - with all that means to a lack of easy readability - work. I would be surprised if Cannadine saw this small book in any such grandiose comparative light in particular because Said wrote about Orientalism, the operative word is 'orient'. Cannadine is writing about Ornamentalism, the operative word being 'ornament'. I don't know how can confuse the two - probably only if you haven't read either book.
This book is short, and maybe slight but what Cannadine has to say explains, or at least adds an important perspective on the British Empire, how it was ruled, and how it ended - and the way it failed to create sustainable government structures in so many of the colonies they withdrew from. It actually follows on from an observation, almost casually, in his 'Decline and Fall of the British Aristocracy' about how the aristocracy withdrew, or were pushed out, of so many positions of influence and power in the 19th century but how a upper class 'culture' and 'style' - that really was a way of thought, dress behavior, etc. - remained and was transmitted through the public schools and particularly Oxbridge to define what an Englishman (even if he was actually from one of the Celtic countries of Britain) was. This group 'think' and 'style' meant that the Empire was run by suburban boys who were unable to cope with the reality of a changing Britain and went off to find a pre-industrial world of grand seigneurs and noble peasants to run - or many cases create. It explains in many ways why - though the ruling British in any colony - would talk of wanting to educate and uplift the poor 'benighted' natives - the colonial British almost invariably hated any native with education and did everything in their power to have nothing to do with them and if forced to have contact treat the educated 'native' with an insufferable contempt. What colonial Britons liked to do was spend time with 'unspoilt' natives and their 'natural 'chiefs'. The consequences in places like Nigeria, post independence, was awful in terms of war and bloodshed.
Of course this doesn't explain everything about Empire and doesn't mean that racism wasn't a huge
influence - but it does help to explain how so many men (and in terms of power it was only men at that time) who weren't superficially monsters or bad ended up doing so much harm when they thought they were doing good. It also helps explain, in part, why so many non Britain's when viewing the Empire saw only monumental hypocrisy.
Of course you need to read other books about the Empire, how it was formed and ended, obviously avoiding the ridiculous pro-western pro-USA tosh that Niall Fergusson has written (such a disappointing writer/historian - his early books were so good) but I recommend this one for all its faults and limitations as it will give you interesting perspectives and much to think mover.