The trick, I think, is picking the right character.

I wonder about that. I don't imagine Alan Moore had any desire to write Swamp Thing before he got the job (not that I have any way of knowing if this is true or not), but once he got the assingment, he channeled his genius through a pretty lame character. I mean, I read the Marty Pasko/Tom Yeats version of Swamp Thing that preceded Alan Moore's, and it really didn't look like very promising ground.