Most disappointing aspect is easy: it is completely redundant.
Really, what was the point of it all? The ST was compressed into one movie already: Return of the Jedi. So I guess I have to give Johnson credit for realizing that when he made TLJ and killed off Snoke - essentially saying “we already killed the Big Bad Guy 2 episodes ago remember?” TROS undid this and remade ROTJ - thus undermining Luke’s character arc, as well as Anakin’s (for those who consider the PT canon). Rey is now just Luke…only better (or worse - since Luke defeats evil with Faith/Love, while Rey uses lightning). Thanks to TROS the entire ST is just a reboot of the OT. NO POINT!!
Quoting myself is lame, but I wanted to add this quote (from a youtube comment of all things!)
“If you don’t stop at Return of the Jedi, you have to commit to perpetuity.”
For me the most disappointing aspect is they worked this very thing - the perpetual nature of it all - into the story as a reason for extending beyond ROTJ, but then they completely undid it in TROS.