Nexus is one of the best books I have read in years. It had a fast paced plot dealing with the morals and ethics of our transhumanist future along with a nice bit of Buddhist philosophy. Also the unique setting of a cyberpunk Bangkok was pretty awesome. Crux is the sequel novel that deals with the aftermath of the events in Nexus.
There isn't much I can say about the plot without somewhat spoiling Nexus but I will say that we find the surviving characters of the previous novel each dealing with the new reality from those event in their own ways. They have changed the world in ways both good and bad and might have a few chances to make things better. In the end the book is about the good and bad impact transhumanist technology can have on a society. Technologies that are developing in the real world much faster than anyone would have though just a few years ago.
The most common complaint I have read about Crux is that the quality of writing isn't very good. Although I see what those reviewers are talking about and Crux isn't going to win any awards for literary style, I feel that these critics are missing the point of a book like this. It isn't about the quality of the prose, but the quality of the ideas which is important. This is the major reason the Sci Fi tends to be viewed poorly by literary types. Crux might not win over the literati but I feel that Ramez Naam is a solid writer and he is able to depict action scenes much better than most other authors.
This leads to the major complaint I have with this book, and something I have noticed happening in most modern Sci Fi. I felt the book had too much action and didn't focus enough on the ideas. The novel could have been significantly shorter if many of the action scenes had just been left out with no real damage being done to the story itself. Additional character development, world building, and just random musings on the social impact of the various technologies in the book would have been a welcome change of pace from the action. It almost feels like Sci Fi writers today are scared of their audience getting bored and that blowing something up is a way to fix that.
I also didn't feel that the anti-transhumanist characters were given enough depth and space to give their side of the argument. Some rather horrible things are done in this book in the name of humanity and the people committing those acts end up looking more evil than rational. It may be that Ramez Naam decided that Nexus gave enough of that argument and that Crux should instead focus on the real possible implications of transhumanism. Even if that is the case I felt more time could have been given to debating the issues that the book brings up.