This doesn't quite reach the level of pop-science for me. It's a quick read (I read the first 115 pages or so in one sitting). However, I was probably only understanding about half of what I was reading. I found myself understanding the broad strokes of what NDT was trying to convey, but not the details.
I agree with an reviewer who said: "I suppose it isn't easy summarizing astrophysics in 200 short pages but this could have been better. He frequently does not explain certain concepts and ideas." I found there were too many concepts mentioned in a single sentence without any further explanation before NDT quickly moved on to another topic.