Kevan is waaaaay more sympathetic to his brother than Tyrion or other characters, who despise and fear him. But we know, he did love his wife, a particular reason why he loathes Tyrion, and he did smile once. But, he never remarried, one would think that Lord Tywin would take the opportunity to use it to his advantage. He never does. Perhaps that says something about Tywin Lannister that all the other characters miss.
I think KoP summed up power really well in one of his blogs: "Power is an image, after all." (Yes, I'm a semi-fan/stalker KoP, deal with it xD.)
What Martin did was give us the Tywin everyone else saw, the Tywin that was feared, respected. Tywin, Hand of the King and the *real* power behind Westeros. We never saw who Tywin the *man* was, only hints here and there.
One scene which baffles me even today is *SPOILERS*
Shae in the Hand's bed. I'm not sure what was going on there, but it seemed by Tywin did enjoy his ****s, which made him kind of the biggest hypocrite in the series. Unless I totally misunderstood that scene. (I was sucked into the moment, it all went by really quick.)