Overall, Kevin seems like a solid guy. He respects Dana's wishes, offers her support, and makes a genuine effort to learn whenever she tells him he's wrong. But he can also be defensive at times, especially when he feels like he's being blamed for something he can't control. On one occasion, he talks about slavery and Dana gets angry: "I turned to glare at him and he looked back calmly. It was a what-do-you-want-me-to-do-about-it kind of look" (3.7.47). In other words, Kevin is all for learning. But at times like this, he can only just shrug.
Kevin's sense of morality eventually lands him in hot water when he gets stuck in slave times. As Dana notices after they're reunited, "There was a jagged scar across his forehead—the remnant of what must have been a bad wound. This place, this time, hadn't been any kinder to him than it had been to me" (4.16.37). Kevin risks everything to help black slaves escape to freedom while he's in the past.
When Kevin returns to 1976, he has a lot of trouble adjusting. The book says, "With a sudden slash of his hand, he knocked both the sharpener and the cup of pencils from his desk. The pencils scattered and the cup broke" (5.1.84). By the end of the book, Kevin is a changed person just like Dana. He can never forget the horrible things he's seen and he is very happy to know that slave owners like Rufus Weylin are all dead and gone. He's a nice guy, but his sympathies only go so far.