We don’t get a solid description of the monster, but apparently he’s horrifying to behold. What? Did Frankenstein make him ugly on purpose?!

Isn’t it explicitly mentioned he tried to make it beautiful but it all looks wrong once it’s alive? This part specifically:

His limbs were in proportion, and I had selected his features as beautiful. Beautiful! Great God! His yellow skin scarcely covered the work of muscles and arteries beneath; his hair was of a lustrous 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 of the same colour as the dun-white sockets in which they were set, his shrivelled complexion and straight black lips.