I'm 100% alright with Rey beating Kylo during the lightsaber battle. Luke and Anakin both did impossible things through the Force when they were untrained, why couldn't Rey? Besides that, Kylo Ren doesn't seem very disciplined, and I'd be willing to bet he didn't finish his own training before falling to the Dark Side. His adoration of Vader's accomplishments and complete disregard for Anakin's return seems to have given him delusions of grandeur about the Dark Side, and I've never really considered the Dark Side to be stronger. It makes sense to me that Rey got the drop on him this go around, but I'm fully expecting an Empire moment next movie. He'll come back and he'll be better prepared.

Speaking of the Dark Side, I love how Rey was tempted by little things throughout the movie, like selling BB-8 for more food, and how easily she overcame these temptations, but during that fight it seemed very likely that she was Dark for a bit, but stayed completely in control. It's probably a stretch, but the fan in me was going nuts during that fight.