If it's crap ... We'll tell you
You have a point especially if you look at the fact that the beginning and the end of the movie he's always in a symbolic underworld whether its in the ground or in a bowling alley his actions is malicious and that's why he always stays in a hole or be under ground.
My favourite example of of a character devolving has to be Charlie Gordon played by Cliff Robertson in 'Charly'. In many ways he advances and regresses at the same time.
I didn't think the movie did Flowers for Algernon any justice, but that's just me...
I can understand what you mean but I see it as a separate animal. Sort of a relative of 'Flowers' but not necessarily a direct descendant. If I looked at adaptations as anything other than a separate entity influenced by the vision of others involved I'd probably be one of those people who keep crying foul when their favourite property has been altered.
So you want people to post examples of a very famous trope?
He became disillusioned. He went from an idealist to an oprotunist.
Oh yeah! Also Edward Jessip in Altered States.