I think you will get a great deal of variance on this answer. I think the monster was human. Indeed, it was created out of scientific inquiry, and might not have followed conventional conventions as to how humans are created. Perhaps, this is a notion of genius on Mary Shelley's part in her assertion that science is a transformative element and individuals have to be ready and willing to embrace such change in order to abide by the full dimensions of scientific progress. I think that the monster's human qualities are reflected when it sees others playing in the small hamlet, aware that it will never enjoy such company and joy. At this moment of self consciousness, the monster is irrevocably human in that it is aware of its own condition, and feels that pangs of it. The idea of being a "hideous progeny" is what motivates it to ask its father, Victor, to create a companion. It seeks to evade the pain at the heart of all: The pain of loneliness and abandonment, two things it experienced at the hands of its creator/ father, Victor. Indeed, the monster does do some fairly inhuman things, but it would not be the first time that a human being acts in a manner that is less than human. I would suggest that these elements of seeking companionship, possessing self awareness, and wanting to alleviate its own tormented condition are what helps to define the monster as human.
Physically, the monster is not quite human; he is made up if body parts, and his living essence is drawn from electricity. These two facts contribute to his 'monstrousness' and the notion that he is less than human or even inhuman. However, the monster is intelligent, compassionate, articulate and thoughtful. He converses with eloquence and logic. He is also very aware of the fact that his physical appearance is frightening to other humans, and this fact is frustrating, hurtful, humiliating and distasteful to him. The fact that the monster has human thoughts, feelings and emotions contribute evidence to an interpretation of him as human, and more significantly, express a primary theme of the story, that humanity does not lie in outward appearances but in what lies within each person's mind and heart.