I promise I'll get to the plot, just let me gush about the worldbuilding a bit first: wow! Garth Nix once again presents a place I'd want to live in. It's a sci-fi setting that focuses on three areas of technological advancement: psychic interfaces, biological engineering, and boring mechanical stuff as well. I'm a sucker for a good bioengineering book, but they don't seem too common. (You've got the Leviathan series, Next, this, and that's all I've stumbled across.)
But as promised, my opinion of the plot: the main character felt a little generic. I didn't get a strong personality other than 'naïve' and 'arrogant'. He got into problems, but didn't struggle much to escape them. The problems themselves were interesting, just not the protagonist's response. If you can live with a bad plot every once in a while but need a good setting, then try this book.
In some ways I hoped Garth Nix would come and make a sequel in the same world but with different characters to try and redeem the plot.