First, I'm no great crime novel/thriller reader. However, for me the plot frankly was a minor attraction, I very much enjoyed this book for all sorts of other reasons.
The characters are interesting, unique in my experience. The picture of Thai life & culture, & of Buddhist belief, is (particularly to someone previously largely ignorant of these things) fascinating.
Does the book deal in stereotypes? No, I don't think so. Some of the characters appear stereotypical when you first meet them, yes, particularly the "tormented US spy", but, they don't conform for long, they have their own subtleties. Most are complicated, if not downright strange.
As to its authenticity, it certainly appeared very true to life to me. I've never visited Thailand, & others have offered opinions on how close to reality it is. For my part I'll say that nowhere did anything strike me as unbelievable, or false, quite the contrary.
This is my first & probably only review by the way, so I'll finish by saying it is shocking in places, amusing in others, informative, & overall quite wonderful.