It's a very broken, badly damaged Palpatine. If Plagueis taught Palpatine how to influence his own midichlorians to somehow survive his own force lightening and the fall down the pit when Vader tossed him in, then he'd have still been badly damaged from it. Maybe only just barely surviving it. And since we didn't actually see Palpatines body (we saw only an energy blast near the bottom of the pit after he was tossed in) it's safe to assume that he similarly escaped in a way that Luke survived after he dropped into the pit on cloud city. Now, look at the picture of Palpatine after his self inflicted transformation in Revenge of the Sith. Notice the deep skeletal ridge line running vertically up and over his skull. Also the brow line had puffed up in size as well. He had a grayish colored skin also. Now look at the side by side CG pictures of Snoke floating around the Internet. Notice he has the grayish skin. Now notice that the left side of his face has been horribly damaged and scarred, to include some heavy loss of muscle tissue in the cheek and jaw line. Also notice that the once centered ridge line in the skull has been twisted to the left side as well. Almost as if the skull itself had been partially crushed and twisted and merely healed back that way. Snoke/Palpatine's face is severely twisted and sunken on that left side as well, likely from tissue and bone loss as well as nerve damage. As we saw in the movie , he seemed unable to move anything on the left side of his face, including his mouth. Also his once puffy looking eyebrow ridges are now fully deflated looking. His right eye also droops noticeably so. Here is a man that saw some severe physical trauma in the past. But he IS strong in the dark side of the force. It is possible that he somehow escaped the Death Star before the explosion. Most will argue how it is impossible, however, did you actually SEE Kylo Ren or Gen. Hux escape star killer base? No. But it was implied by Snoke. It seems a likely outcome that he was biding his time while he recovered. And it is highly likely that he influenced Ben/Kylo through the force in his early years. Only someone who knew Vader personally could tell Kylo of how Vader failed his mission because he was seduced by the "light side" of the force. And Palpatine was a master tactician and manipulator and had the patience to wait out everything in his rise to becoming the emperor. Everything went according to his plan, except his own supposed death. Now he's back, masquerading as Supreme leader Snoke. All the signs are there that he is Palpatine. I could be completely wrong, however. But I can tell you with utmost confidence that it sure as hell ain't Plagueis.