You'll get more info as you progress...

It was an okay book, but not particularly groundbreaking. Gaider is a good writer, I think, but I have to agree with Yiasemi and Xetirox, in that his writing vs. some of his public statements... I think he suffered from what a lot of Hollywood script writing hacks suffer from - that they have a character who is doing bad things - and they can't "own" that - they end up trying to make the character somehow just "misunderstood" or make attempts to soften the bad things he did. I love a nuanced "villain", I don't need the red-eyed evil overlords. I wish Gaider/Bioware had just let Loghain's late in life irrationality and paranoia, which brought the nation to the brink of civil war, cost him his daughter and ultimately the respect of the very people he claims to want to protect.
I have seen, particularly on Bioware's forum, people going on about how Loghain is not evil, that the game will have you understand why. Fine, he's not "evil." But he's paranoid, ambitious, irrational, deeply angry (and actually, in the book referenced above, his constant undercurrent of anger is probably the character's most consistent feature. imo.) Ultimately, he's dangerously misguided and lost the pulse of the people and ignores the larger threat (darkspawn invasion) over the paranoid hatred (however justified by his past) of the Orlesians.
Basically, any case for Loghain being anything other than an irrational, powerful, angry [censored] gets immediately broken by the game actions.
Spoiler Howe's treachery PRIOR to Ostagar, wipes out one of the strongest nobles in the land after the king - and his later access to Loghain speaks of a prior arrangement. Loghain allowing the only legitimate son of his late king and life-long friend (as well as the child of a woman he loved, Rowan) to be slaughtered on the field. This was also his beloved daughter's husband.
If his quitting the battle without participating was to be justified by seeing that the battle was already lost -
Spoiler he's supposed to be an amazing commander and strategist - if he could see the way things were going, he would not have waited on a bonfire signal. He would have known something went wrong when it was taking too long. And afterwards, why go to great lengths to outlaw and blacken the name of the Gray Wardens? He sends an assassin after them, he has people looking out for them, and a bounty on their heads. He is tied directly to trying to poison Eamon, a powerful and influential political noble, and the uncle to the slain king. All of that speaks to a naked power grab. Why couldn't Gaider just "own" that.
Even at the end, when
Spoiler you get the opportunity to allow Loghain to join the Gray Wardens, his justifications for his behavior are pretty lame, given the other evidence. He even dismisses his daughter as a drama queen... and yet, when you find her at Howe's, the Arl has taken the step of making sure she is imprisoned with magic, not just a locked door. Regardless of the annoying Anora's personal ambitions, if you are the supposed Queen and were imprisoned by someone you went to to discuss your concerns about your father and the current political situation, who is supposedly your father's closest advisor, I'd be a little nervous about what might happen next.
I think they ended up trying to wiggle out of the fact that they set it up so that Loghain snapped, and his loyalty become horribly skewed, at a cost of many lives...
Spoiler maybe because they wanted a possible crisis point for Alistair, or just to create drama around allowing Loghain to live. Frankly, I enjoy the hell out of the game in spite of sloppy plot gaps, but other than once, for the sake of just seeing what happened, it would make no role-playing or story sense for either the Warden or Alistair to be anything but "no way does this guy get to live for what he's brought us all too".