I hate it when Trek books go through all the rigamarole of establishing a long-dead aspect of the history of some culture, only to totally destroy it and have it not matter at all in the end. ("Oh shit all the priceless historical artifacts got blown out the hull breach! Guess we won't be learning anything from that!") This book at least leaves part of the ending (the serum/Orion leadership) ambiguous, but unless this chick shows up leading the Orions again in Vanguard or something, it pretty much has to be a non-starter.
Plus, for being a novel set in such a big gap in Trek history, it did basically dick-all to give us any new information about either galactic affairs or particular characterizations. Spock's tendency towards run-on sentences was a joke more than a character trait and kind of dumb, and no one else exhibited any real characteristics of any kind. Even Boyce was sort of McCoy-lite. The Lost Era novels gave an incredible sense of the many decades of history through which they ran; this told me nothing at all.
All in all, the alternate universe aspects of it weren't interesting enough to be worthwhile, it also didn't tell us anything new about the prime universe, and the story was a giant dead end with some false ambiguity added on. I'm not the biggest fan of standalones in general, but even still I think this was a pretty bad one.
Inception, Unspoken Truth, and this have been a pretty uninspiring run of TOS novels. I am not very impressed.