Seeing that there are numerous summaries of the book, this review shall focus almost purely on my reaction to the book and reasoning behind the score I gave it.
Having watched the film (and, admittedly, enjoying it), I did some reading on it and found out that it had been a book. Written more than a decade ago, there is something to it that seems so modern and hardly came across as dated science fiction. I thought the characters were well developed and the books mixed Western and Eastern tradition very well (although it did seem like Mr. Tsutsui alluded to Western thought as being a vehicle of corruption via it's effect on Dr. Inui, however this is debatable and a point you may be able to see after reading the book).
I had a very difficult time putting down this work and really enjoyed reading it. I couldn't help but sense, however, that something got lost in translation.
My reasoning behind the 5 stars I'm giving the book is based on readability, enjoyment, creativity, intelligence, and the difficulty level of putting it down. It was fast paced with hardly a dull moment which made reading it throughout a joy, rather than a chore. It's a very creative concept and I thought Mr. Tsutsui did a wonderful job developing the characters and the who concept of a D.C. mini, taking such a simple idea that many of us have thought about (looking into someone else's dreams) and bringing it to life in such a realistic (and terrifying) fashion. As a major of Psychology at a University level, I found this extremely fascinating and think he did a great job psychologically developing the characters and thought the concepts he used to be very fitting.
So, my only regret to this is that I am forced to read a translation (which can never truly do any literary work justice). It makes me wish I had studied Japanese so I could reap the full enjoyment of such a wonderful tale.