There's two things I judge harshly on. The inability for one to admit when they are wrong, and lack of courage to say I'm sorry. That tells me all I need to know. Because we are all wrong at some point. But not all of us are sorry.
Lack of friendship in a marriage is what really kills it. If you haven't married your best friend then you're doing it wrong. "It is not a lack of love, but a lack of friendship that makes unhappy marriages.