I've had 24 hours to digest the movie now, so have a couple of theories on issues people brought up:
#1 - I was surprised that they actually did cover a back story for Snoke, at least a little bit. There were growing tanks in one of the scenes where Palpatine was creating the shell for Snoke bodies. I took it that Snoke really is just a mouthpiece for Palpatine. He didn't really have story other than that and his disfigurement was all just part of the Emperor trying to create an organic, force sensitive shell. I'm sure he was running a variety of different experiments with all the time that he had.
#2 - How did the Emperor survive ROTJ? Still something of a mystery, but I think there's a clue near the end. If Rey and Ben and Baby Yoda can summon life force to heal wounds, I think Palpatine can too, but directing the energy back into himself. You see him regenerate his hand in seconds and he's further regenerated after blasting Rey and Ben. So, after his fall on the DS, he could have likewise summoned the life energy of others on the station to regenerate. He could likely get to a ship from there or Mary Poppins himself through space if he had to I guess.
#3 - The Knights of Ren. These guys had almost no purpose. They seem like Ben's entourage, but then side with Palpatine at the end because...? Maybe he was controlling them the whole time as well, but that seemed odd to me.
#4 - Lando wasn't a coincidence. Pretty sure he says that Leia sent him to warn the others. He could have been on the planet already or near the system. His role was mostly behind the scenes, but someone had to get the word out to the other systems to come help, so that was a good use of the character in my opinion.
#5 - I think the Jannah character was added because Rose is such a terrible actress. That role was just to give Finn some acceptance of his own past, so they left Rose at home and added Jannah instead. Not a pivotal character, but I can see why they added her.
#6 - I thought it was weird that they skipped most of Palpatine's son/daughter storyline to go directly to Rey. Maybe he inseminated lots of women and most of his offspring didn't have force powers, but granddaughter Rey did? That seems like a big plot point to just leave out.
#7 - I don't understand why Han is very nervous about jumping into the atmosphere of a planet in TFA, but Poe can jump from one world to the next with just meters to spare without hitting anything or causing adverse effects? Suspend belief there I guess.
#8 - Why does the Falcon "crash" when the landing gear fails? It doesn't have wheels to land like a plane, so couldn't it just hover and set down awkwardly? That scene kind of bugged me.
#9 - I always took it that Palpatine kind of "fathered" Anakin, which would mean in a way that he somewhat created the Skywalker line. If that's true, then aren't Ben and Rey like 2nd cousins? The theme of cousins and siblings making out in Star Wars movies is a little odd.
#10 - Force Ghosts make no sense! I still don't understand how Yoda can shoot lightning or Luke can hold a lightsaber in their "astral" form. If so, materialize near Palpatine and make a building fall on him and you'd avoid all this fighting. I did hear a theory that there is a difference between a force ghost and the ability to actually reincorporate for a limited amount of time, which would give them physical abilities, but that still seems odd. Or, did they know that Palpatine would transfer his essence into whoever killed him, thus making him supremely powerful if he transferred into a form that could dematerialize and reform at will all around the galaxy? Hmmn....
#11 - BONUS - I really liked the take on Palpatine having all the Sith "with him" in conjunction with the power to transfer his essence into his successor. Seems like that's the Sith plan all along set up by Bane and the reason for the rule of 2. When the Master dies, he actually joins with the apprentice, making each Sith stronger and smarter than the last.
