What types of mood and atmosphere are found in the book Frankenstein?

I would say the primary mood/ atmosphere in Mary Shelley's Frankenstein is one of foreboding or dread. Consider, for instance, that we get most of Frankenstein's story after the events of the tale have occurred; in other words, Frankenstein is telling us his story retrospectively, allowing him to reflect on his story as he tells it. Thus, it's easy for him to infuse his tale with a strong feeling of dread and ominous foreboding, as he already knows what happens. Moreover, it's clear from the start that Frankenstein's experiments are a bad idea and will only result in something evil, and the monster's stalking of Frankenstein and those closest to him builds a sense of dread. All in all, the story has a mood of building terror, and we get the sense that we as readers are also being haunted by some monstrosity. That said, it's hard not to sympathize with the monster once we meet him. As such, the mood also involves a sense of melancholy, or even tragedy.