That is silly and of course she is a MARY SUE, her powers come all to quickly and easily, that is what MARY SUE stands for, look it up. Another silly point about this new movie is that a lightsaber can cut through layers of metal in a Star Destroyer (Grevious' ship comes to mind) but simply scratches flesh? I'm a big SW fan and the OT should have been the last of it. Star Wars has too many people involved now, It's bigger than it really is. When asked about the new movie Geaorge Lucas wouldn't answer but his face and look of disappointment said it all. His baby is someone else Bi*** now. Not to be a spoiler for the next movie but apparently Han Solo comes back with bionic legs, you didn't really see him die, he simply fell out of sight. Lando was waiting below to save him. Movie Magic.
To be fair, quoting the prequels for anything is a recipe for disaster. Take that lighsaber cutting power example. In the classic movies, it's shown a few times that saber hits on metal will not always cut through it, look at the railings in the Cloud City duel or the Emperor's Throne Room duel. Sure, they eventually do get cut through, with a very powerful strike (IE : Vader's angry riposte after getting injured, and Luke's final blow against Vader's arm) but the rest of the time it just makes sparks, like it happened in TFA. The prequels making sabers able to melt through ten-inch metal doors is absurd and silly.
About Yoda, yes he had to fight the Emperor. But did he have to use a saber? No. In fact Yoda's philosophy relies on the fact that you don't need weapons to do the right thing, and I'm sure the duel would have been better with only force powers, like when he slams those two royal guards against the wall. That was the only good part. Sidious should not have used a saber either, especially considering how disdainful the Emperor was of sabers in general in ROTJ. It's clear Yoda and the Emperor, as masters of their sides, should have grown beyond the use of such a limited tool and only used powers. The sabers are for the grunts, like Luke and Vader, far below that level of mastery.
As for the whole Mary Sue argument, a Mary Sue is a character without flaws. I loved TFA and Rey's portrayal but she definitely had flaws, such as being stubborn to the point of getting in trouble by only following her own plan, getting very scared of getting involved in bigger events / getting away from Jakku, getting angry during the final duel.. she's a more nuanced character than she is given credit for by some people, but it is quite funny to see that most of the people who hate this movie are people who fervently defend the prequels, as if to say "LOOK! A new Star Wars movie! Go hate that one instead of hating my precious prequels!"
To each their own, but I'm sure the new trilogy will be remembered for something more than ruining a legacy, the same cannot be said for the prequels.