I kind of find the Punisher interesting because more than any other fictional character I can think of (even beyond comics), he is an expression of what the author thinks of the world, more than he is his own character -- "Frank Castle" is more of a set-up for future action than he is a fleshed out personality, pure background details to justify his competence in violent situations. Basically the author picks out whoever they think are the worst, most vile motherfuckers on the entire planet of earth, and then they have the Punisher kill the shit out of them as catharsis.