A fascinating weave of neuroscience, artificial intelligence, and the philosophy of mind.
Kurzweil presents the pattern recognition theory of mind (PRTM), which holds that the fundamental unit of computation in the brain is a group of ~100 neurons in the neocortex that recognises a pattern. The clever part is that these patterns can exist within arbitrarily complex hierarchies, containing "pointers" to other patterns, and feeding input/output to both sub-patterns and parents.
It's a nice theory and seems to explain some empirical findings in neuroscience, though I would defer to a domain expert to comment more on that. Some of his arguments seem quite suspicious: for example, he often justifies his view of how the brain works by implementing the procedure on a computer – according to Kurzweil, if it works on a computer, that is likely how it works in the brain.
The second half of the book is somewhat disorganised, covering the whole gamut of standard topics within the philosophy of mind: computation, consciousness, free will, identity, etc. Nevertheless, it's a highly accessible introduction containing plenty of references to famous thought experiments and philosophical writings.
The chapter relating to the "Law of Accelerating Returns" is scary. Humans consistently misunderstand exponential growth trends and the result is that the future will come much faster than people realise. Kurzweil convincingly argues that within the next twenty years, we will have reached the singularity and that by the end of this century, cybernetic enhancements will be the norm.
Well worth a read if you are interested in neuroscience, AI, philosophy, or futurism. This book is an excellent complement to sci-fi books dealing with uploading consciousness (e.g. Greg Egan's Permutation City) – which may not be fiction for much longer!