I adored this book. I got it from my local library and am now buying my own copy. However, I would add that I read chemistry at college and was recommended it by another chemist. It is not a particularly difficult book, I want my 14-year-old to read it, but it is much more chemistry than biography.
It also made me think about what is missing now the practical element has been taken from the education system in the UK now; if you want to inspire a bright teenager this is the way to do it (I particularly like the passage about the 3lb lump of sodium and the local pond - I won't spoil it for non-chemists).
The biographical detail is interspersed with chemical passages and potted biographies of Sack's favourite chemists from the past. The thing that stood out the most though, was the sheer excitement of living through science as it was refined and discovered. There was no atom bomb when the book started, that came along the way. One of Sack's uncles had a scintillation gadget with a tiny amount of radioactive substance that emitted radiation you could see. There is an excitement and enthusiasm not found in many books now.
As well as being gripped by the science, its application and the history, I found it an extremely well written book. I want to read his neurological books as a result.