Victor Frankenstein's descriptions of his 'creation' are nearly as disturbing as anything I've ever read:
It was with these feelings that I began the creation of a human being. . . life and death appeared to me ideal bounds, which I should first break through, and pour a torrent of light into our dark world. A new species would bless me as its creator and source; many happy and excellent natures would owe their being to me. No father could claim the gratitude of his child so completely as I should deserve their's.
For all his descriptions of this "new" life, Frankenstein never does call it good.
This account is, in the novel, reported in hindsight by Frankenstein, and so he is able to reflect, only a few pages later, immediately after he animates the creature: "It became a thing such as even Dante could not have conceived. . . I felt the bitterness of disappointment: dreams that had been my food and pleasant rest for so long a space, were now become a hell to me; and the change was so rapid, the overthrow so complete!"
For two years of working on that creature, Frankenstein understood himself as God, and so naturally once his goal was achieved, he found himself in Hell. He had been there all along.
The epigraph of the novel's title page is borrowed from Milton: "Did I request thee, Maker, from my clay/To mould me man? Did I solicit thee/From darkness to promote me?" So spoke Adam, after the fall. While the connection there is certainly between Milton's and Shelley's creatures, Victor Frankenstein's realizations--after the fall from that heavenly throne he had established for himself--assure us that Mary Shelley also remembered well Milton's Satan:
Which way I fly is Hell; myself am Hell;
And in the lowest deep a lower deep
Still threat’ning to devour me opens wide
To which the Hell I suffer seems a Heav’n
O then at least relent: is there no place
Left for repentance, none for pardon left?
Paradise Lost, IV. 75-80