A triumph of a book. Reflected in it's Hugo award and the fact that I have probably read this book 6 or 7 times in my life. Of course, the point of this re-read was to put it in context with the rest of the Company Wars output and it still seems like a triumph of a book, cast in that light.
This book is set after the Company Wars and explores the Union society that was kept largely as a faceless enemy in the Company Wars sequence. The Union is a designed society using designed humans (called azi) to bolster its population as it terraforms the world it started on (the titular Cyteen) and expands into space. This is very much a book told in the 'historical fiction' mould, in fact it always reminds me of Michener in his pomp (having that thought again has prompted me to put Centennial, Space, Chesapeake and Texas on the re-read list) as it is told in a very similar style to how he approached this kind of thing.
At root this is a book about 'nature versus nurture' using the artificial humans as the lens for the exploration. However, the lens is not just applied to the micro (ie the azi), it is applied to the designed society as a whole. The Union is a designed society, this contrasts with the Alliance (at the forefront of all the other Company Wars books) and distant Earth which just kind of happen. The book is an exploration, not an endorsement of one or the other and is stronger for that.
For extra fun the book's plot engine is lots of crunchy family drama type shenanigans just to keep you moving along the exploration of the history and politics.
This is definitely 'thinking' science-fiction of the highest order and has not aged at all. Highly recommended from me.