Does Satan's character fall apart by the end of John Milton's Paradise Lost?
I'm looking for evidence that Milton made Satan charming at the beginning so that the reader would be attracted to him, but let his likability fade at the end so we would come to loathe his evil.
This is a good question.
One starting point is biographical: Milton was a devout Puritan, and unlikely to have admired Satan. The reading of Satan as the "hero" of "Paradise Lost" originates with the later English poet William Blake, and does not draw on Milton's beliefs but was part of Blake's own self-invented religion (Blake himself was rather disturbed and prone to hallucinations).
At the beginning of Paradise Lost, Satan is a charismatic figure (he needs to be to convincingly lead angels to rebel against God), but we can see his pride and ambition. By the end of the poem, his true character has been revealed. I think we do need to assume that Satan has a sort of slick charm -- thus his effectiveness in Christian accounts at corrupting people -- but of a sort that should warn off people who are not themselves proud or greedy.