I've never been a koan kinda guy. Of course, I'm still a beginner at all this zen stuff, but so far I've missed the whole point of a question like, "What is the sound of one hand clapping?" or, "What was your face before you were born?"
To me, it all sounds like a bunch of gobbledy-gook.
There are zen questions that have helped me, though. Zen Master Dae Gak talks about the primordial practice of listening, and of finding one's zen mind through sound, and sometimes asks zen questions related to that practice. In chanting dharani, he had us chant "Old MacDonald Had a Farm" as if it were the Heart Sutra, which at first struck me as rather koan-like. His point was that it's not the words that matter, but rather the practice itself.
But Zen Master Dae Gak also teaches that the basis of our practice - the core of what we do as practitioners - is zazen. Koan practice, liturgical practice, chanting dharani, sutra copying, whatever, is secondary to the practice of seated meditation.
What I know from my own experience is this. When I sit, if I can set my mind free of the formation of words, and then sit long enough to free myself of the formation of concepts, I sometimes experience a wave of something like joy, like a very strong sensation of peace and simple elation. Sitting in zazen is difficult for me, but if I reach this point I can sit there as long as I want. Sometimes it's not joy, not any emotion at all, almost like being free of the burden of emotion. This is when it's really good, when I feel like this is what I was meant to be. Before the pollution of advertising, junk food and road rage, before the stress of finding a job before they take the house, or of getting to work on time, day after day - this is what I was. I'm getting back to my original self. Maybe, just maybe...this was my face before I was born.