I will admit it took me a long time to read this. Even though I'm a science geek, a lot of the concepts do go over my head. It doesn't make it less interesting, it just takes me longer to try and grasp the concept or just give up and move on.
HHDL takes some of the concepts of science and compares and contrasts them to Buddhist practices. If you are interested in either, then this is probably a good book for you. We're taken through the Big Bang vs the Buddhist beginningless universe, Quantum physics and relativity vs Buddhist emptiness, evolution vs karma, several chapters on sentient consciousness vs neurobiology and finally into genetics vs the entire human race.
In the concepts I did grasp and make notes on, HHDL makes excellent parallels between the scientific world and the spiritual world, something that the majority of religions maintain cannot happen. HHDL is all to happy to point out the similarities and encourage scientific progress, but with warnings of keeping the human compassion and ethics along for the ride.
HHDL has often said that every human on this earth is the same, and should all be treated with compassion. He was essentially proven right when the human genome was finally sequenced.
In his own way, he implores (nicely and gently) for society to get better educated about science so that we don't fear it and so that we do not cross a line. "We must be willing to be revolted when science - or for that matter any human activity - crosses the line of human decency, and we must fight to retain the sensitivity that is otherwise so easily eroded."