The Question and Answer section for Frankenstein is a great resource to ask questions, find answers, and discuss the novel.
From what we know of Walton, he seems to be a reliable narrator. Walton is quite sincere about his feelings, even when they are less than flattering. The tone of his letters implies homoerotic longings, which, at the time, were certainly taboo.
One of the themes in Frankenstein is creation. For a complete list of themes and detailed explanation of each, please visit Gradesaver's theme page for the novel.