I'll answer your question concerning Shelley's Frankenstein by looking at a different element or side of nature.

Nature vs. Nurture is a central theme in the novel.  Left to himself, without nurturing from his creator/father, the creature turns into the monster.  Victor fails his responsibility to take care of, to nurture, that which he creates. 

The wild, natural man, then, does not turn out so well.  Victor rejects him largely due only to his appearance.  As a result of this rejection, the creature suffers from isolation, loneliness, emotional deprivation, and eventually becomes a monster. 

Unusually, and perhaps ironically, the creature, left to fend for himself in the world of nature so emphasized by other romantic writers, does not absorb its goodness or touch the transcendent or commune with it and experience transformation as in, for instance, Wordsworth's "Tintern Abbey."  Nature does not lead the monster to acts of kindness.  His isolation leads to acts of horror.