Short version: The author knows a lot of facts about James Kirk but understands nothing of his heart or soul.
Longer version: I've seen all 79 episodes of TOS many, many times, and the James T. Kirk I saw in those episodes is NOT the man portrayed in this book. The Kirk in this book is full of angst, paralyzed by self-doubt, and constantly tortured by his lack of a stable romantic relationship. He's also a mean-spirited jerk who tries to break up OTHER people's romantic relationships because he has none of his own and is jealous of theirs.
Does that sound like Kirk to you?
I don't know how Goodman got the contract to write this book, but he was the wrong guy for the job. He clearly knows a lot about Star Trek in general, but he has completely missed the heart and soul of the character he claims to be portraying.
Yes, we do see in "The Naked Time" that Kirk misses having a stable romantic relationship. But to take the things Kirk said while he was not himself because of the polywater intoxication and generalize them as being the One True Thing about Kirk is a mistake. Yes, we do see Kirk have moments of self-doubt, such as in "The Apple," when he second-guesses himself about not having aborted the mission after the first death. But those are MOMENTS of self-doubt that exist to humanize the character; that self-doubt isn't perpetual!
The man I saw prowling the bridge of the Enterprise is a bold and confident man who absolutely adores being the captain of the ship. He's a tactical genius and a persuasive orator. He's a man who treats his crew like family and who is, in turn, adored by them and given everything they have. Unfortunately, that man is not present in this book.
While Kirk never gets to have a stable romantic relationship, he does have deep and important relationships in his life. Though they're not romantic (in canon; I know there are LOTS of fanfics that say otherwise :-D), his friendships with Spock and McCoy are deep and important relationships that do much to fill his heart, and he considers those two men his family. Those relationships are given short shrift in this book; their importance in Kirk's life is occasionally stated but rarely shown.
Kirk's childhood and family background are adequate, though I have trouble picturing the Kirk we know coming out of the background he's given here. But I'm a clinical psychologist in real life, so I accept that what I consider to be a realistic background may not be the same as what other readers would want. :-)
Aside from the mis-characterization of Kirk, the book curiously flat. The book makes the Tarsus IV tragedy ... not terribly emotionally affecting. Over and over again, events are portrayed, but most of the emotional punch that should go with those events is absent. The author writes clear prose, but it's not very affecting.
This book is a grave disappointment, because it misses the greatness of James Kirk and makes him a much smaller, weaker, and more mean-spirited man than we know him to be. I wish Spock had neck-pinched the author while he was writing it, so that this travesty had not been foisted on the public.
For a recent Star Trek novel where the author DOES understand the characters, I recommend Dave Galanter's Crisis of Consciousness. In fact, that probably deserves a review of its own, but two posts in one day is already a lot. :-)