No one has ever denied that Game of Thrones
is closer to its source material than a great many adaptations. One hardly could, since the immediate response to any criticism tends to be "But it might be so much worse!" Yes, it might. It might also be much better, both in terms of adapting the interesting, dramatically complex aspects of the source material and as a television series in its own right. I'm not judging Game of Thrones
as a fantasy adaptation; I'm judging it as a prestige HBO drama, which it pretends to be. And on those terms, it falls short. The source material is only relevant to that insofar as it sometimes offers more complicated and less usual takes on fantasy tropes that the show ignores in favor of the obvious thing.
There's a separate issue here, of the way minor details play a key role in a work that deconstructs a genre from within, so that an adaptation that's 95% faithful can still omit the elements that make the underlying material distinct, but I'm not sure I have the time to tease it out now. It's also true that some aspects of the story are treated much more faithfully than others, so that readers will have different perspective on faithfulness depending on which parts of the books mean most to them.
Orientalism, by the way, is a term with a fairly specific meaning, and its only real applicability to Essos is the general notion of a mysterious east of which Qarth is the tip. I'd be the first to take issue with the way Martin writes the Dothraki and Slaver's Bay, but buzzwords don't really clarify the problems involved, which have more to do with his taking a pick-n-mix approach to creating cultures and not thinking about the implications of doing so.