This was so beautifully written and so intense to read, I had to take it in very small stages, but maybe a lot of that depended on personal experience. I know the area where the book is set, I know about intercultural relationships under stress (ouch!), I even know some autistic kids. I've been trying to think how it works to people who don't have those connections with the subject matter.
I was okay with the alternation between the main story thread and other historical bits though I can imagine some readers not liking it. I think it is a bit frustrating that the book never really commits itself to a viewpoint on whether there is something supernatural going on at the pinnacles or whether it's just 'people' and coincidences. Especially after what happened with Raj - I share Jaz's views on that! The book forces you to make your own hypotheses, with no possibility of knowing whether you're right. But I didn't mind that too much, especially because I think it's part of the author's point.
I certainly agree that the openness of the ending is very frustrating. The spoiler below basically tells you the ending, then tells you why you won't like it, so click if you really want.
I could accept Jaz's disorientation and the fact that the story isn't really finished, maybe will never finish. I was fine with that. What disturbed me was the literal cliff-hanger - because to me, the novel ended with the protagonists' stranded in the desert, where I think their lives at risk (ugh, been there, done that too!) and I keep asking myself 'did I miss something? Is the thing that will happen next supposed to be obvious and I didn't get it?' And also, this isn't the kind of story where their death would be consistent, but actually, what would be consistent? Kunzru, if I ever get my hands on you, you will get such an interrogation!!
It is very, very well written though. I guess I gave it five stars because I have a very high tolerance for authors causing me pain and frustration, provided they write beautifully.