Dr. Frankenstein is obsessed with pushing the boundaries of scientific knowledge to "unfold to the world the deepest mysteries of creation." His ambition to be the first man to create life is all-consuming. During the process of putting the monster together, he focuses on the magnitude of his achievement, rather than what his creation will be like once it is living and breathing.
When Frankenstein first sees his creature come to life in chapter 5, physical repulsion is his overwhelming response. He declares,
Now that I had finished, the beauty of the dream vanished, and breathless horror and disgust filled my heart.
His sole reason for this horror is that the monster is "too horrible for human eyes to behold."
Frankenstein claims to be at a loss to understand why the monster is so ugly. He says that he chose the body parts carefully to ensure that his creation would be attractive:
His limbs were in proportion, and I had selected his features as beautiful.
This may well be the case. If so, the monster's disfigurement proves that while Frankenstein is trying to play God, he is not in full control of the process.
On the other hand, it is important to remember that it is Frankenstein who is telling the story here. We only have his word that he tried to make his creation beautiful. It is easy for readers to imagine Frankenstein choosing the body parts quickly, impatient as he is to get on with the task of bringing them to life.
Frankenstein's is partly caused by the fact that his imagination could not picture the end product of his experiment. He became so obsessed with the "beauty of his dream" and the glory he would achieve if he succeeded that he seemed to give no real thought to how his creation would look in the flesh.
Frankenstein uses a variety of dramatic phrases to describe his creation's monstrousness, such as "daemon," "miserable fiend," and "the devil." His choice of words implies that the monster is not only ugly but inherently evil. Eventually, the monster does go on to commit evil acts, partially justifying Frankenstein's declaration that
Alas! I had turned loose into the world a depraved wretch, whose delight was in carnage and misery.
When the monster first comes to life, however, there is nothing to suggest that he deserves these accusations. His only "crime" is to be unsightly in the eyes of humans. It is only when Frankenstein abandons his creature and sends him out into an uncaring world that the monster begins to fulfill his maker's prophecies.
Through Frankenstein's reaction to his monster, Mary Shelley arguably condemns the kind of blind ambition which prioritizes progress over moral responsibility. By attempting to create life, Frankenstein transgresses natural boundaries. He arrogantly appropriates the roles of creation (the preserve of God) and childbirth (the preserve of women). It is little wonder that the results do not turn out as he expects.