Aikido seems more like a medium, just as oil painting is a medium for Art. People can express themselves through Aikido just like oil painters can express themselves through their paintings. What matters is the individual expression.
I have to (respectfully) disagree with this, Ted. I think that Aikido is more of a method than a medium. The point is to develop myself, not express myself. We practice because we are not satisfied with ourselves at some level. If Aikido can be thought of as a manner of self-expression, it is like Omori Sogen wrote of shodo; by writing characters (or doing techniques) we see ourselves more clearly to understand where we need to develop. However, the point is the development, not expression.