I loved it. Much much better than Jane Austen Book Club. I had already read about the twist in a review before I started it.
I particularly liked it as I'm a psychologist and had to study a lot of those twin studies and chimp studies, and I used to want to have my own twins to conduct long term developmental experiments on, so I enjoyed the bits about the postgrad researchers doing experiments and Rosemary picking up all the chimp behaviour.