This is going to be a weird comparison, but I'm willing to put my two cents in:
To me, both games are like playing a game of chess, as both games require thought and aptitude given rather 'stressful' situations. You have to be able to act under pressure, keep your cool, and formulate a defensive/offensive to effectively counter your opponent.
However, while both games are similar to playing a game of chess, I would venture that CoD:MW is the equivalent of playing chess against another human being, while KF is like playing against a computer.
Why?
It strictly comes down to the driving force of the opposing team. In CoD, you are fighting a large swarm of human controlled characters. This offers the dynamic of human error/ingenuity and provides a much more compelling conflict. Moments such as, "What the hell is this guy going to do next?" arise, as suddenly you have to make instinctual counter-judgments based on your opponent's strategy.
In KF, you are simply blasting away at AI-driven drones. They have no strategy, and they simply move in a "Point A to Point B" fashion, reacting purely upon YOUR movement. On top of this, because your character wields a projectile based weapon (in stark contrast to the specimen, which have no projectile attacks whatsoever) it becomes quite apparent that keeping your distance/kiting is a blatant advantage. In other words, unless you are gaming in a confined level, on hard/suicidal (where the specimen's health grows to astronomical proportion) it becomes painfully obvious that you are taking part in a very one-sided fight.
Despite all that, I've consistently found KF more 'fun' than CoD:MW from this very simple point:
When I play video games, I'd like to relax and feel good.
CoD:MW is too hectic an experience for me in that aspect. Don't get me wrong, I love that game to pieces... But when it comes down to it, I can only play it for a couple of rounds before I start to feel mentally exhausted. I get the same feeling from games like UT3 and Counter-strike. Couple that sensation with the infinite amount of text-spammers/mic-ragers, and I've had enough.
KF lets me start up a simple game and enjoy fragging hundreds of specimen without any pressure. It's co-op, so if the team gets slaughtered, it's everyone's fault equally. I can choose how I want to play, because I can either camp and wait for the specimen to come to me, or I can run around and bring the pain to the specimen.
I don't know, just the way I feel about each title.