I thoroughly enjoyed this book and feel that it completely surpasses the previous book, 2001: A Space Odyssey. The writing style is immensely better and the plot doesn't drag on as much as it did in 2001. 2001 consistently had long scenes that went on and on, or numerous sequential scenes in which not much seemed to happen.
Not with this book. The plot is continually moving, adding more action and intensity to the situation, and there are numerous characters (both American and Russian this time) who add a lot of variety and personality as well. The book also answers a lot of the questions we're left with at the end of 2001 while still leaving me scratching my head at the end and wanting more. If you've read 2001 and haven't gotten to this one yet, I highly recommend you do.