If you get past the language, which can be a bit of an issue, not because it is difficult, but because it can become a bit tedious, especially given the preference for reported speech over direct speech, and a certain limitation of vocabulary, Frankenstein regales you with the beauty of its structure of stories within stories, a bit like pictures containing other pictures, of narrators narrating other narrators’ stories, which makes the reader lose the perspective on what is true and what is not, which is at the centre of the novel.
It also regales readers with a feeling of doom , the feeling of the fight of humanity against powers too big for our scale to comprehend, and a series of themes such as the growth of science, ‘playing God’, being a parent, education, the need for companionship, appearance vs reality, physical appearance and real personality judgementalism etc.
Where I think Frankenstein is relevant to gay literature is that it portrays the ‘different’, the Creature (not monster, please!) as amiable, as not so different: the difference is in Victor’s eyes, as well as in the reader’s eyes. In this, the novel is a classic in acceptance, not a surprise coming from a real lady like Mary Shelley.
FRANKENSTEIN ON AMAZON