I enjoyed Zero History the least, but that was entirely because I read it years after the other two, and had a hard time remembering characters from the previous books. I knew it shared the same protagonist as Spook Country, but I didn't expect it to be so twined with its predecessors.
Also, thinking of Spook Country, I really loved it halfway through when the storylines converge in Vancouver. I already lived here at the time, and its sense of place lined up with my sense of place, to the point that I could place the characters on my mental map. It was so unexpected yet bang on.