This book is not very good. In fact, it is just plain awful. It pains me to say that since Michael Crichton is one of my favorite fiction writers to read. Part of this book (Crichton's last), was found unfinished on his personal computer after his death a few years ago. Therefore, it is co-written by some guy named Richard Preston (?). I'm wondering if all they found on this book was a title and introduction, and then said, "go with it, we're sure to make money." - It should be noted, Crichton's book Pirates: Latitudes was also discovered posthumously, and it was a great book!
At any rate, here's the plot in a nutshell. Some evil corporate types/scientists have discovered a technology that can shrink objects and people... blah... blah... blah... mix Honey I Shrunk the Kids with Jurassic Park and you get Micro.
The thing that has always made Michael Crichton's science fiction enjoyable was his in-depth scientific research, compelling thriller narrative, and just barely beyond believable plot... The things that makes Micro awful are the shear unbelievability of the story, the poor character development, and disjointed storyline...
bottom line: don't waste your time.