This is a great book to read as preparation for a trip to the Galapagos. It's based loosely on a BBC TV series, but ends up being a primer on the islands.
The book goes over the geology, history, and ecology of the islands. It doesn't get much into the current political situation- there are other books for that.
The book prepared me for the weird landscapes that encompass the islands. The climate when we were there was arid (last part of the dry season in late November) and the place seemed desolate. You could see why, historically, no one was eager to claim the territory for themselves. Little fresh water, little fresh meat except for the tortoises (sadly), nothing to make you want to stay. A tropical paradise this is not. The poor marine iguanas were called "imps of darkness" because of their coloration and appearance, and superstitious sailors felt that the islands were cursed.
These islands are like nowhere else on earth, and this book gave me the background to see them in context with the past and with some of the current environmental issues. The islands have been devastated by invasive species, which now make up over two thirds of life on these islands. Different subspecies of tortoises, birds and iguanas have gone extinct, unable to compete with robust alien animals which arrived on the islands as purposeful imports or accidental stowaways.
Even though the islands feel almost alien, they do have a beauty to them. And this place was the genesis of Darwin's concept of evolution, a theory which changed the whole world. It's hard to overstate the importance of the concept of life that can change to how we have interacted with the world. It's led to advances in medicine, greater understanding of ecology, geology, astronomy. No longer do we believe that we live in a static created universe; we know that we live in one that's changing all the time. (At least, a lot of us do think this- many people do beg to differ.)
The last part of the book was hugely practical for my family, which did a land-based trip in Santa Cruz instead of a boat trip. There are lists of animals and which islands they live on. Also a run-down of what each island is known for. This gave us a good basis to plan our trips to neighboring islands to view wildlife. I read three books in preparation for our trip, and I'd say that this one was the most useful.