If you enjoy pondering this question you should definitely check out the works of Stanislaw Lem. One of the main themes of his work is that alien life would be fundamentally different from life as we know it and that human consciousness, bound by the concepts that we use to understand our own world, would be unable to comprehend it. His novels contain a lot of imaginative examples of that kind of alien life, the most famous perhaps being the planet in Solaris.