I also liked the book. However, Tuvok's role wasn't as big as I expected (comparing to him being on the cover, having a whole paragraph on the backside and starting the novel with his backstory).
The actual conflict, using the device being good/bad, was pretty much left open in the end. I would have wanted Tuvok to fight a little more for his decision to mind meld and pro/contra keeping/destroying the decive.
Furthermore, what about that conscience? That was pretty much dropped at the end and didn't seem to play a big role anyway.
Or are those threads for the next TITAN novel? Then I didn't say anything and I am looking forward to reading it. :-)