Major spoilers, enter at your own risks
1) Leia was a Jedi, trained by Luke, has a light saber of her own but it was never shown with her, later was given to Rey by Luke (force ghost). In this movie Rey was trained by Leia.
I don't think that was planned from the beginning. Otherwise why did Rey seek Luke in the first place? Couldn't Leia have trained her from the beginning?
2) There was no explanation how Palpatine came back, other than "dark side has many abilities".
3) Rey is Palpatine's grand daughter, which from what I see it, quite hard to explain considering just how old Palpatine was.
4) In this new movie Palpatine asked Rey to kill him so their spirits would merge. And Palpatine was the merged result of all Sith. Rey refused and Palpatine regained youth (well, not as old as before at least) and strength by sucking the life force out of Rey and Kylo (That is new). Rey defeated Palpatine by channeling all Jedi (think witches in "The vampire dairies").
5) Rey immediately died afterwards (exhausted from the channeling?). Kylo revived her, Rey kissed Kylo and Kylo immediately died afterwards with a smile on his face, seem to be the consequence of resurrection. The whole thing felt arbitrary.
6) Palpatine had an entire fleet of planet killing star destroyers, but they all parked in close formation without shields, so they were just sitting ducks. I can not think why they were not properly deployed.
7) Force ghosts in this movie can hold light saber and lift aircraft, so I don't know why all the Jedi force ghosts did not gang up on Palpatine and did nothing to the first order.
8) All Skywalkers died in this movie (the end of Skywalker bloodline and heritage). In the very end Rey found Vader's uncle's abandoned residence, seemed to want to settle there (not opening Jedi academy or anything), and changed her name to Skywalker, probably ashamed of Palpatine heritage.
The entire movie felt empty, corny and ridiculous.