My wife and I love everything having to do with blood, guts and horror. Getting her to play was as easy as showing her a screenshot of the game. 3 years later, and we're amped up for the full release! We've cleared our schedules for this Thursday, so we can play the entire day away!
The great thing about KF that has consistently spoken to my wife is the lack of competitive atmosphere. Nobody rages over the microphone, "YOU SUCK!" or anything to that effect. Because you're facing AI, there's no feeling of inferiority when you get killed, and nobody has to impress anyone.