I didn't have a problem with Rey defeating Ren - By that time, Ren was pretty worn down himself. Also - Rey is a backwater junkyard scrapper. She knows how to fight - Not with a lightsaber, but with melee weapons in general (Like Finn), with assistance from the Force. Also - Ren is totally hitting on her because he's a hormonal emotional teenage boy.
I really liked that the Stormtroopers and Tie Pilots were actually competent this time around. Not quite as competent as they should be (Finn, being one, was able to handle too many of them too easily, IMO. Then again, it may have been a situation he could hard-counter them, and he knows their (And his own) training). I liked that NONE of the TIE fighters destroyed themselves on the wreckage during the Millenium Falcon chase, though it tried telegraphing that result several times. Instead, the TIE fighter pilots are "Half-mad crazy obstacle course run after a broken-down freighter? We've totally got this, man." I figure the only reason they didn't win there was A.) Plot Armor but possibly B.) They didn't want to take any shots that would destroy instead of merely disable the Falcon. Unlike the Death Star Plans, they needed that Map Section intact.
I also liked the fight between Finn and the Stormtrooper. Apparently, Laser Sword beats Rifle in CQC, but Finn was no more or less trained than any other Stormtrooper. That fight made it clear that Finn was a trained CQC combatant using a weapon he was unfamiliar with, so he was fighting at a disadvantage, lost, nearly died, but did manage to get rescued. But the CQC training (Exhibited by both himself and his mirror-match-up) foreshadowed his ability to fight, but not triumph over, Kylo Ren.
Also - I really hope that in the sequels, Rey ends up with a double-bladed lightsaber similar to her spear she's trained with.
EDIT: Wait, that wasn't Coruscant and the other Core Worlds destroyed by the big gun? Damn... that takes all the relevance out of the scene. I could have sworn that was them blowing up the previous movies.