I've always enjoyed Sam Harris's works. His works make you think about who you are, your assumptions about the world, and the conclusions you've drawn. You don't have to agree with him, but his works are thought-provoking nevertheless.
With this in mind, I found the content of the book to be deeply disturbing. Over the short course of about 1 hour, Sam Harris makes the case that you are not the author of your own actions. He argues that, based on research, your mind makes decisions before you realize them. This was the part I found unsettling.
That being said, I do think he went a bit too far with this one. Personally, I don't think we understand enough about the mind to make such conclusions. Yes, there has been research done that DID find that the areas of the brain that make decisions make them milliseconds before your conscious mind realizes you've made them. However, there's also been recent research that suggested the fact that your brain makes connections in 11 dimensions. So, we don't know as much as we think.
I certainly wouldn't say I wasted my time reading it, but I wouldn't recommend it to someone else. There are definitely more consequential works that I would recommend reading first.