*** SPOILERS ***
I agree that they were a LOT of reused ideas from Episode IV (kid from desert planet, hiding info in a droid, a Death Star, X-Wings launched to attack as the Death Star is about to destroy their base) but I wasn't too bothered by it. In the end, both Finn and Rey are very interesting characters and the movie was incredibly entertaining.
About Kylo Ren, I like that he's not a clear cut bad guy, still conflicted about the dark and light side (I don't like that he looks like Josh Groban though). I think that killing his father troubled him more than he thought it would which is shown by the fact that Chewie was able to land a shot on him so in the final confrontation he's shaken and wounded.
*** EXPANDED UNIVERSE SPECULATION AHEAD ***
About Rey, my guess is she's Luke's daughter (which is why they limit her backstory to a minimum). I know they said the EU has been thrown out the window but it seems it might have just been rearranged. Leia and Han had three children in the EU one of which turned to the Dark side (Jacen), Luke had a son named Ben with Mara Jade (a former disciple of the Emperor).
From what we saw in The Force Awakens, Ben is the only son of Han and Leia so maybe Luke's child is now a daughter, Rey. She could have been hidden on Jakku after Kylo Ren turned to the Dark side and destroyed the other apprentices.
All of this to say, she might be so gifted with the force because she's the combinaison of both Light and Dark, a perfect balance.
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