If you are like me, meaning your brain refuses to understand or remember scientific facts, this is a great book. It is very "big picture" about our understanding of the world, and made me want to do some more science reading. I was always frustrated in school (particularly during physics) when we spent a long time on ideas that we now know to be wrong, but Bryson makes the history of science interesting by giving details about what strange (and often petty) people scientists were and are. It also helps to show that we have so much left to learn.
There is no thesis to this book, so unlike Guns, Germs, and Steel, which hits you over the head with a point over and over again, this one just keeps moving. If there were a thesis it would be: scientists are weirdos. Bryson's writing is easy and enjoyable—many of the blurbs refer to his wit, and here is one more:
"Bryson's wit is as sharp as his tongue: pink, and covered in beard hairs."