I love the Rey character, though I am somewhat critical of her speed of doing certain Force things. It's different than Luke in one major regard: Luke did have Obi-Wan tutoring him while he was learning to use the lightsaber, and even after Obi-Wan died during the trench run. He had the advantage of at least seeing Obi-Wan perform the jedi mind trick, just as an example, and then he was able to ask about it. Rey did these things with no (as yet revealed) prior training or exposure.
It's different.
You could certainly say (and I would accept, to an extent) that it has been established that certain characters are just naturally using the Force even with no training at all. Luke presumably channeled it while bulls-eyeing womprats (not much bigger than 2 meters!) and Anakin did it while piloting his pod-racer. That natural ability could have also certainly helped Rey wield the lightsaber (along with her own training with her staff). But using specific Force techniques without any tutoring? It's a bit too
fast forward for me. Nevermind that between A New Hope and The Force Awakens, we've had a lot of expansion in the series about what Jedi training actually encompasses.
That said, go back to the first sentence. I love the Rey character.
It's not even that she uses the Force, because it's already subconsciously helped her dodge blows that would've otherwise killed her as she was running away. But it's when she consciously channels the Force at the end, she channels the dark side. That whole part of the fight isn't filmed, staged, or scored heroically. It's intentionally uneasy with Kylo Ren getting thrown off his balance in slow motion, Rey hitting him while he's down, her gritting her teeth, taking hard swings. She's channeling her rage, unaware of how dangerous this is. The ground separating the two of them is purely to prevent her from going too far.
Dark side? I don't see that at all. She had such a look of calmness come over her at that moment, total serenity, and then she unloaded.
Also, I grit my teeth when I'm in the gym. That isn't rage, that's determination, because I'm doing something hard.