In Frankenstein, how does Mary Shelley control our views of the monster in the opening letters and chapters?
Let us remember that the monster as you call him is only created in Chapter Five, and so the opening chapters include little or no reference at all to Frankenstein's creation. However, what you might like to focus on is the way in which Chapter Five presents the monster and in particular his maker's reaction to it. Consider the use of the first person point of view and how it helps present the monster so that we see it through the eyes of Victor Frankenstein:
How can I describe my emotions at this catastrophe, or how delineate the wretch whome with such infinite pains and care I had endeavoured to form? His limbs were in proportion, and I had selected his features as beautiful. Beautiful!--Great God! His yellow skin scarecely covered the work of muscles and arteries beneath; his hair was of a lustruous black, and flowing; his teeth of a pearly whiteness; but these luxuriances only formed a more horrid contrast with his watery eyes, that seemed almost the same colour as the dun white sockets in which they were set, his shrivelled complexion and straight black lips.
It is clear that Frankenstein is attracted and apalled by what he has created, especially the way in which the beauty of the creature contrasts with the horror that is evoked through his "watery eyes." Given the choice of point of view here, we can say that Shelley is allowing our impression of the creature to be shaped by Frankenstein's own biased impression, though we can also argue that later on in the novel, when the creature is given speech to express his own point of view, we are presented with another, very different way of considering him.
Ok so - Walton's letters are a framing device to (a) create pathos between the reader and Frankenstein who represents himself to the sea captain as a victim to his situation, (b) to authenticate Frankenstein's claims before he dies and (c) to make the monster more inaccessible, and thus more frightening.
Frankenstein consequently narrates the novella in first person, and obviously presents himself in a positive light as a man of science and the Enlightenment. In actuality, Frankenstein really does a horrid thing by not acknowledging his creation...but our sympathies clearly lie with him.
But as we know, science and morality sometimes do not mix.