I saw this topic the other day, so I went and bought the book. I never read any of the other stories, so this was fresh to me.
A few things bothered me (see below), but overall, I think it was a good book. First 200 pages were a bit slow but decent. Once Spock becomes Emperor, it picks up pace and the rest is fantastic.
Here are some thoughts on the book:
Things that I didn't like:
1. Tantalus field is just too powerful. Absolutely ridiculous. The original episode gave you the impression that the thing works by taking out one person at the time, and there is no evidence that it works at long range. The book made it out like you can kill anybody in the known galaxy as long as you know their location. Imagine, you could assassinate the entire Romulan senate, Klingon council and invade the leaderless empires. Hoshi Sato took the advanced Defiant to Earth and became empress with a single ship; why didn't Kirk take Enterprise with the much more powerful Tantalus field, kill the senators and proclaim himself emperor? It doesn't make self that in Mirror, Mirror he's skulking around insignificant planets and doing ordinary missions as a mere captain.
2. The inclusion of too many familiar characters. Trying to "weave" everything together is not always necessary. For example, Captain Terell, the ever-present Duras, Elaan of Troyus...they were too much. Familiar characters are good, but not too many.
3. Why are other races not alternatives as well? It appears only humans are different in the other universe. Romulans, Cardiassians, and Klingons are unchanged.
4. It's a bit hard to believe that so many ships were mothballed and disarmed right before the Alliance attack. I just couldn't buy it. It would have seemed more plausible if the gov't was wiped out by the trillithium device, and then disorganized military junta and chaos that followed lost to the Alliance. In a way it would have made Spock's calculations a little off and made him look imperfect. I mean, remember that episode of DS9 where those genetically engineered humans predict fall of the Federation and nobody except Bashir listens to them? It would have been nice if Spock realized that he was wrong and that things might not turn out the way he calculated. It would make the next book less predictable and more interesting.
Things I liked:
1. The scene on Trill. I read that it was borrowed from another novel in the afterword. I don't know the extent of borrowing, but it was my favorite scene in the book. Reminded me a bit of 20000 leagues Under the Sea.
2. I like the idea that Sato was cloned and her dynasty went on like that. I would have liked to read more about it. Why didn't she have children? May be it's in the other books...
3. The politics of transfer from Empire to Republic were excellent (Spock's and Sarek's plan). I do wonder how the conspirators were found out though? The assassination was planned from the top, including the director of SF intelligence?
4. The final scene with Spock and Marlena was great. This scene could have been somehow kept even if number 4 from above happened.
All in all, I wasn't disappointed, even though it completely contradicted William Shatner's books