Eyes I was just about to post something along those lines when you beat me to it.
I assumed when I first saw ESB (with the original Emperor) that Palpatine was maybe a non-human and almost certainly really, really ancient.
Come ROTJ he seemed to lose some of that really weird anti-Yoda quality but still looked like a truly ancient human (so old that he would defy even the anti-agapic technology available in a galaxy far far away, that only his will power was keeping him alive).
Doctor Who fans out there may be aware of a story called The Deadly Assassin which not only preempted The Matrix films but depicted the Doctor's arch foe in much the same state as this model of Palpatine in ROTJ (passed the point of regeneration his body is so ancient it's falling apart but his hatred is keeping him together despite his infirmity) :
(Ok so it looks a bit goofy but Peter Pratt does wonders under that mask and it was done a year before ANH on a shoestring budget)
For that to work Palpatine would have to be already very old in Episode One.
If he had been around for a very long time and saw the Republic already beginning to fall apart he may have been seen as a safe pair of hands when the Clone Wars started (like keeping Abraham Lincoln alive until the modern age and assuming that he would be the ideal person to lead America through the Cold War).
The Dark Horse Dark Empire series postulated that using the Darkside drains the vitality out of Palpatine so he has to keep decanting his essence into fresh but fast decaying bodies (another survival technique the Master used in Doctor Who).
The ROTS explanation for Palpatine's appearance was the most daft and pointless.
It seemed that Lucas felt the need to show a wrinkle faced Emperor and a polished perfect ESB Vader at the end of ROTS because that's how the audience recognised them.
We have already scene Vader's suit change in the relatively brief period between ANH and ROTJ so why didn't we see a more primative version of the suit in ROTS?
The same with Palpatine, it could have been expained by showing him using his powers more and more towards the end trying to defeat the remaining Jedi so by the time we see him in ESB the strain of trying to keep his Empire together has resulted in a prematurely really ancient looking mummy of a man when in fact he is just very old (but not that old).
The Halloween mask seemed to be the cue for Ian to throw all the subtlety of his performance so far out of the window with Mace Windu.
He went from this clever puppet master and a joy to watch and listen to a parody of his ROTJ performance (which was more than a little OTT to start with).
In a more general Wishlist I would prefer the ROTJ Emperor to be the culmination of decades of increased decay (much like Tiberius' arc in I Claudius).
Having him just turn into a prune because of a Force Lightning blowback doesn't make any sense on any level.