There were many things I liked about this universe that he'd created, liked the characters, some of the technology (the implanted software/hardware so you can control spacecraft, etc...).
The concept of the spiritual aspect where the crisis in the book came from.
I did wonder at the time how he was going to resolve it eventually.
But on the whole enjoyed this book very much, which prompted me to go and buy some of his earlier works which I found to be as clever and inventive (A Quantum Murder, The Nano Flower).
The resolution in the third book that he came up with I was a bit disappointed in, but on the whole a great trilogy of books, the first one is still the best though in my opinion.