Excellent hard-sf, it's heavy on (real/realistic) neuroscience. It strands you in the middle of things to figure out what's going on and revealing things slowly.

This is one of those books whose ideas keep coming back to you. What does it mean for something to possess intelligence? Is a very complex ~markov chain bot trained with the all the world's content intelligent? Are humans any different? Is a virus (or a self-replicating robot) life?

Also, has the funniest acknowledgement section.