Back to the topic: there’s so much aspects of the movie that I found disappointing, so I don’t know what the most is, but what I would have liked to see at the beginning of the movie is Rey building her own lightsaber (the one we see at the end of the movie), using parts (the Kyber crystal!) salvaged from Anakin’s lightsaber (which got torn apart in the previous movie). She has the ancient texts, she would have known how to build one, and it should have been part of her training. It would have been ultimately cool to see her fight with an orange blade. (Seeing her ignite her new lightsaber for no reason at the end of the movie is just fan service)
ROTJ deleted scene of Luke igniting his lightsaber for no reason before putting it in R2.