It's his human characteristics, but his lack of emotions. I believe that Data grows constantly throughout TNG, but what I find is that I like him because he is so much like us, but then, really not at all. He is a reflection of us, (although I'm not quite that pale) but he still is very different from us in numerous ways. I find his charater quite intriguing. He walks, talks, and looks like us, but he is an Android. I do, however, argue that although Data cannot comprehend emotions like you and I, he does learn. I sometimes find that you feel emotion from him, even though he insists that he has no feelings.