(or "Shall Not The Judge Of All The Earth Do Right?")
Very few characters have gone through the kind of transformation that the Spectre has gone through over the decades, even before the total revamp of the character in 1999. Actually, the "total revamp" of the character in 1999 was a significantly smaller reworking of the character than the one that had been slowly and gradually performed over the course of the stories that make up 'Showcase Presents: The Spectre' (and slightly beyond, through to John Ostrander's iconic 80s series which has not been collected.) The Spectre's human host changes from Jim Corrigan to Hal Jordan, but his mission as the vengeance of the Lord remains the same...a mission notably absent from the character as first created.
Originally, the character was a fairly standard "avenging ghost" superhero, one with ill-defined and nebulous powers (in his early Silver Age stories, which were written by noted polymath and parapsychology enthusiast Gardner Fox, you see lots of discussions about "ectoplasmic energy" and "negative soul-force", which all seem to boil down to "The Spectre is exactly powerful enough to beat a bad guy by the end of the issue, no more and no less".) The usual stories involved him finding some sort of supernatural evil that he couldn't defeat...for some reason...until he did some inexplicable thing that sounded like someone was regurgitating random bits of jargon that Madame Blavatsky made up, at which point they instantly fell to his awesome powers. (In that respect, it's a lot like Fox's run on 'Green Lantern', except with fewer mentions of the color yellow.)
And like Green Lantern, this poses a lot of problems when it comes to making up ideas for stories. If your hero can do anything, why is there ever a reason for a story to start? If your hero can do anything except when he can't, how can you possibly do a consistent series with them where one story follows on from the next? Limitations are an absolute necessity for good drama, and having to come up with them on the fly on an issue-by-issue basis is utterly exhausting. A good storytelling should be the opposite of exhausting; it should supply you with ideas instead of forcing you to come up with more of your own. A set of clearly defined rules that limits the Spectre's powers and forces him to actually battle bad guys is a necessity.
Or...is it? (Insert musical sting here.) When Michael Fleisher revived the book again as a series of back-up stories, he went with the opposite approach; he removed the Spectre's limits altogether. Fleisher's Spectre had no difficulty fighting, defeating, and even brutally murdering his opponents; the question that defined his drama was no longer, "Can he stop the bad guy?" but instead, "Is it right for him to do what he does?" In this fashion, he removed the question of power and its limits from the equation. The Spectre was now a metaphysical drama, in which Jim Corrigan dealt with questions of whether a man who had come back from the grave could call himself "alive", and a reporter questioned the inherent justice of a universe where a chalk-white figure in a Speedo could turn a man into a tree and then run him through the sawmill. From there, it's a relatively short trip to the iconic spirit of vengeance that Ostrander wrote about and everyone since has made use of.
Obviously, this opens up different opportunities than the Silver Age version of the character; it's not likely that Gardner Fox could have found an audience for a Dostoyevskian exploration of morality as related through the spectral messenger of a vengeful God, even if he could get it past the Comics Code. But it is a character that generates lots of interesting story ideas, because the questions that we ask in 'The Spectre' as it is currently conceived are as old as humanity itself. As long as people do evil and the universe doesn't seem to care, there's a place for the post-Fleisher version of the Spectre, no matter who his host is. And with a new DC Universe, there's bound to be a new Spectre just around the corner.