How does Mary Shelley explore the dark side of the human mind in Frankenstein?

In his obsession to master the realm of science, Victor
delves dangerously into the matters of what constitutes life.  As Victor begins to
surpass what is known, he enters a realm much like that of Satan in Paradise
Lost who dreams of a new world to be created which he may make his own. Like
Satan, too, Victor wishes to take on a role that is only God's; in Victor's case this
is the creation of a living being that is made from human parts.  This preoccupation
with his power to create causes Victor Frankenstein to forsake his humanness; all his
desires turn inward to himself, and he abandons his friends and family to his scientific
acts of construction or destruction.  Victor's obsession with science hinders the
nurturing of his soul and the goodness inherent in him, as the Romantics
believed.

Frankenstein's creature exemplifies what happens
to the human soul when it is renounced and given no spiritual nourishment. 
Interestingly, the creature compares himself to Adam in Milton's Paradise
Lost which he has read: 

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"It moved every feeling of wonder and awe, that
the picture of an omnipotent God warring with his creatures was capable of
exciting."

But, the creature
remarks, he has been given no Eve.  So, since his creator rejects him and leaves him
alone, the creature,then, seeks revenge upon Victor Frankenstein, much as Satan seeks to
destroy the human world in his hatred of God.  Unloved and unwanted, the creature
retreats into the dark realm of his soul and mind and destroys what Victor has loved in
his evil realm of revenge.  Now, he compares himself to Satan,
saying,

"Many
times I considered Satan as the fitter emblem of my condition; for often, like him, when
I viewed the bliss of my protectors, the bitter gall of envy rose within
me." 

 Much like Satan who is
rejected by the beings of which he was once a member, the creature, who through
abandonment by man enters the dark side, seeks to avenge himself upon these
beings. Certainly, in the darkness of their souls, there are parallels between Victor
Frankenstein and his creature; in fact, some view the creature as the dark side of
Victor himself, rather than a separate being.