One naturally expects great things of Isaac Asimov and in this case, one is not disappointed. This is a gripping, thought provoking story of the struggle against human arrogance and self deception. I must confess that once I picked it up I found it very difficult put down again and I finished it within 3 days.
The book is split into 3 parts, and the middle part is some of the most imaginative story telling I have ever come across. It describes a dis-functional family of totally alien beings, with their distinct society, physical drives, biological mechanics and three sexes, set in another universe where the fundamental physical laws differ from our own. The relationship between these beings and our own universe is one of the chief plot devices in the book.
An important aspect for me personally in a Sci-Fi story is that the inevitably made-up science is relatively sensible, and Asimov does not disappoint. If you have a degree in Physics then you may be able to poke a few holes in the underlying theories, but in general the science is very well thought out and well presented.
This is a real Sci-Fi classic.
The only problem that I did have with this book was that I found the ending to be slightly underwhelming. There was some tension building - both scientific and political - throughout the last third of the story and I felt that this tension was swept under the carpet. The climax which I had been expecting never really happened and everything just sort of turns out fine.