I really enjoyed this book and can't wait to read books 2 and 3. David Mack is an excellent author, he brings an Arthur C. Clarke style of mystique to his stories which are well suited to the printed page section of the Star Trek unvierse (be sure to check out the Star Trek: Vanguard series if you enjoy this, two of the three books so far were written by Mack).
The Borg have truly been restored as the greatest Trek foe returning to the relentless and unstoppable threat as presented in TNG. As another reviewer has pointed out you do feel that a major confrontation with the Borg is being held back until perhaps book 3 (but to be fair that would make perfect sense).
Having thoroughly enjoyed the last Enterprise novel, "Kobayashi Maru" it was great to find that Columbia and her crew play a major part in the story (be sure to check that out before reading this too) and ties in well to the superbly executed Enterprise E/Voyager/DS9/Titan crossover.
Although a little slow in parts this is non the less a great read and I'm excited to see how the trilogy unfolds.