I was a big fan of Castaneda when his first books came out. I was in college then. Two years ago, I set out to read all of his books, first to last, in order. I highly recommend that exercise.
This was one of the better Castaneda books. It's always dicey to write about Castaneda and the "r" word: did this really happen?
I am inclined to say yes, but not in the usual way. I know that some might see this as a cop out, but I do believe that we all live in our heads and in a world that we create in there. No one else really has access to our experience except us. What we perceive is what we imagine to be the world out side of us, and our thoughts and feelings inside of us. Castaneda's experiences are as real as anyone's.
Did he make it all up? I don't know, nor can I ever know. If he did make it all up, he was a genius. Who knows? Maybe Plato made up Socrates. Sure, the was a person named Socrates, and maybe there was a don Juan Matus. In the time of Plato and Aristotle, it was quite common to write dialogs about famous thinkers and write what they should have said, or write what they might of said, what was characteristic of their thinking. If the original never actually said that was not a problem. This wasn't our sense of history and truth that we have today.
Ultimately, there is being, what is, and what is not. Truth, falsity, right, wrong, good, and evil are all of the mind. If you stick to facts, what is, you won't find any of the above. "There is nothing either good or bad but thinking makes it so." Shakespeare.
For me, Castaneda, don Juan, and don Genaro are great beings. I enjoy their mystery a great deal.