has a gravelly voice
Palpatine didn’t have a gravely voice in the OT. I’m not even sure why they changed his voice slightly after Mace melts his face off in ROTS.
As for him being mysterious he’s supposed to be that way in TFA. Did you expect for them to lay out his entire backstory in the film? Also his backstory and further development of him as a character could differentiate him from Palpatine quite a bit.