We end up knowing a lot about the Emperor, both from himself and what other characters say about him, in the original trilogy alone.
A pretty telling scene is when Darth Vader, who actually kills subordinates for being bad at their job, points out the Emperor is not as forgiving as he is. We also find out the Emperor is extremely manipulative and secretive, to the point he was able to bring down the entire Republic pretty much by himself and replace it with an Empire all while somehow keeping his powers hidden. How many people even knew Palpatine was able to use the Force? You could probably count them all on one hand.
We still don't really know anything about Snoke. Where he came from, what his plans are, how he acquired the resources he has. For a guy they tease as being as powerful and manipulative as Palpatine, we know nothing about him and he's dead now so it's all pointless to wonder anyway.