This is an epistolary novel, which means the story is told in the form of letters. An objective narrator, Walton, writes letters to his sister Margaret and in these letters, he tells the story not only from Victor's viewpoint but also from the monster's viewpoint as Walton speaks to both Victor and the monster at various times. Walton also inserts his omniscient point of view, so we have three viewpoints in the novel - protagonist, antagonist and omniscient narrator.
You can read more about the Romantic and Gothic elements in the novel at the link below. There is also an interesting discussion of the Doppelganger effect.
The writing style of this novel is even more archaic and cumbersome when the monster is speaking. This is because when the monster was created, Frankenstein fled and did not think about raising his "baby." So, the monster had to learn to speak and read on his own, while he was in the forest. Plus, the first language he learned was French, not English. This makes his speech very formal and archaic because he was reading works like Paradise Lost in English. For example, after the monster kills Victor, he says:
What does it avail that I now ask thee to pardon me? I, who irretrievably destroyed thee by destroying all thou lovedst. Alas! He is cold, he cannot answer me.
Please see the link below for more answers.