I've played this game at least 7 times, and I've achieved almost everything this game has to offer, however just today I finished reading the novels, and they did explain a lot of things to me.
The insight one of them offers on Loghain (The Stolen Throne) is excellent. When I first played the game I could hardly hate Loghain more that I did, after all this guy did horrible things, it appeared he was the perfect villain, and truly was the main antagonist (unless you recruited him) for most of the story.
Cailan on the other hand, seemed a bit idealist, like a little kid who hasn't seen how difficult the world can get, yeah sure he was a nice guy, though he appeared only briefly, and I was surprised that Loghain could let him die that way, after all he was his best friend's son, and like a foster son to him, but well ambition and power do corrupt men.
A man that's gone through everything Loghain did, acquires some bitter memories, he was born on an occupied land, the orlessians forced him and his family into a wandering life, his father was killed by people loyal to the orlessians, things like that make someone capable of loving and hating with such passion that many things would not be understandable to someone who hadn't lived it.
He was a patriot, he became obsessed with power, he may have thought his motives were noble and just, and he believed it, though his distorted vision of nobility and patriotism clouded his better judgement, all in all this novels were a great addition to an already great game.