[Matrixbeast]

I think part of what makes Carnage appealing is his cackling glee.
He was a psychotic serial killer, and he still is a psychotic serial killer.
He's not complex, but he doesn't need to be. He's a roadblock to overcome.

He's not really a good villain in terms of character, but he's effective in terms of character morality, threat, and action pieces.
He's a 90's character through and through, but he's infinitely more memorable for reasons unknown to me. Not being a character with teeth constantly grit, always a stern expression across his face, or trying too hard to be cool, I think he can serve as a decent antagonist in a movie if they remember to keep the charisma he has as a gleefully insane killer.