I am a great fan of technology forecasting (and the Singularity - known as the Geek's Rapture - in particular) and fervently believe in extrapolating today's trends to illuminate the possible paths ahead. While this book has the scientific credibility to power the batteries, the filament (Kurzweil's opinion) is very selective in the future paths that it lights up. It is the author's subjectivity, and unabashed self-promotion that corrode the overall quality of what should have been the definitive post-human road-map.
My main issues:
A basic underlying current moving the direction of the discussion throughout the book appears to be Kurzweil's fear of death. The most frequently cited impact of the technologies he reports, are the ways in which it reduces / eliminates aging. The author is 56 years old (and is quite justifiably proud of biologically being only 40 years old), and constantly talks about how "technology X" currently in development could help avoid death in the next three decades. While it is important, making Ray live forever cannot be the most important feature of the Singularity.
The Singularity is Nearer the West Coast:
Kurzweil makes no attempt to either colour his research, or even explore the implications of the Singularity on anyone not living in California. I found this such a strong theme that it almost felt like chauvinism. The way in which he suggests the Singularity will change life are all to do with how people on the West Coast of the USA currently live. The ideas and projections would be far more accessible had he sought to stretch his horizons beyond San Diego / San Francisco.
Kurzweil is so optimistic he ignores completely the negative, but very human aspects of our intelligence - aggression, xenophobia, greed, hierarchy - and talks of post-humans as being saintly, benign gods working to the benefit of all pre- and post-humankind. The benefits of AI (and the Genetic / Nanotechnology / Robotics technologies in general) will almost certainly be used initially by a very small elite, to propagate their own aims and objectives above those of others. This is the story of any fundamental advance in human history - he does not explain why this most fundamental of all advances will be any different. Surely, those able to achieve a post-human state first will benefit the most, and therefore remain ahead of all others. Kurzweil does not address this topic - the onset of the Singularity, and implications of trickle transcendence - in depth anywhere.
Way too long:
The ideas encapsulated in the book are important, and the author goes into them in some detail - which is essential. While technology forecasting is by its very definition speculative, it is not structured at all well in this book, and could have been made far more accessible. In each chapter Kurzweil will speak in detail about a particular research group or theme - these sections could have been tabulated, showing probabilities of success, impacts on the singularity timing or aspect, etc - this would have made the overall view far easier to grasp, and the act of speculation much more scientific.
Bottom line: Some good - most bad. Based on this book, the only geek getting the Rapture is Ray!!