Quote 1: "Never did i behold a vision so horrible as his face, of loathsome yet appalling hideousness." Page 276
Even though a specific judgement wasn't made in this quote about the monster, it shows how terrified Walton is of the monster.
Quote 2: "A fiendish rage animated him as he said this; his face was wrinkled into contortions too horrible for human eyes to behold; but presently he calmed himself and proceeded—(17.6) Page 183
He believes that the monster is too horrible to look at , and that's exactly how everyone sees him
Quote 3: "`Accursed creator! Why did you form a monster so hideous that even YOU turned from me in disgust? God, in pity, made man beautiful and alluring, after his own image; but my form is a filthy type of yours, more horrid even from the very resemblance. Satan had his companions, fellow devils, to admire and encourage him, but I am solitary and abhorred. (15.8)' Page 164
Even the monster recognizes the fact that he's alone because of the way that he looks. He's upset because even his creator is terrified of him because of his appearance.
Quote 4: "You are in the wrong," replied the fiend; "and instead of threatening, I am content to reason with you. I am malicious because I am miserable. Am I not shunned and hated by all mankind? You, my creator, would tear me to pieces and triumph; remember that, and tell me why I should pity man more than he pities me? (17.5) Page 182
Even his own creator would kill him because hes so terrifying and ugly.
Quote 5: "But presently my rage returned; I remembered that I was forever deprived of the delights that such beautiful creatures could bestow and that she whose resemblance I contemplated would, in regarding me, have changed that air of divine benignity to one expressive of disgust and affright." (16.32) Page 180
He knows that he'll never be treated nicely by other people because he's not considered beautiful like this.