Liked the first book, thought the second one was average and this one was poor. I'm surprised because, even with all the problems I have with modern trek, Mack's books are generally always pretty good even if I don't agree with all the story-telling choices.
Number of issues:
* The scale of the main threat was so big as to largely meaningless, I just couldn't bring myself to care
* The "see you round ending" with Gatt was WTF??? even given Data's promise to him and his aboutface ("gosh I was wrong about everthing!") that was so simplistic that it would shame a He-man cartoon
* The romance sub-plot was equally simplistic and was the sort of material you expect in to see in a poorly written YA adventure - I think the reason that I find Chen such a terrible character is that the writers seem to have this tendency to write her as a 14 year old girl in her personal life and the level of emotional complexity she displays because of that is the level of a kid as well. Again, when we got the denouncement, if this was live action, the characters would turn and look directly at the viewer. It just came across as filler.
* The solution to the main problem was intended to be epic and cosmic but just came across as a bit silly and felt like "oh shit, we've got a few pages left, let's wrap this up"
It was just a very poor book all round and I'm really disappointed that the Fellowship (who are a very interesting concept) were wasted in this story.