This is not a review as such, but contains a piece of information which none of the other reviewers have covered. Much SF is simply discussion of human history in an alien guise. The issues covered in this book are the old arguments about the merits of 'civilization' vesus 'savagery', and what to do about it (Or, if you like, the idea that one way of life is better than another). The older, imperial idea that colonization was the way to spread 'civilization' is out of favor with many people now, but some of these same people support it in other ways. Such as claiming that 'women are oppressed and every one must save them' from some traditional society, which their own multi-cultural principles say they should leave alone.
'The Gray Prince' is a book which explores these themes, but it is rooted in a specific case, of which I think many of its readers are unaware. It is this: the whole development of the plot is heavily influenced by what happened in the 1970's to the African country of Rhodesia (now known as Zimbabwe).
Learn about Rhodesia (taking care to note *all* the different points of view) and see if you do not agree that this is what Vance is doing.
I give the book four stars because the development of the 'clash of cultures' theme is very good. It misses a fifth star because of a flaw which is endemic to many SF stories; containing actual different races of sentitent beings, which may well have different needs. Therefore, in this type of story, racial thinking actually has an objective basis in fact. On Earth we have only one race, the human race, so stories about real, different races do not apply perfectly.
Still, I have to admit, that did not spoil 'Lord of the Rings' for me.