Rey's power level surprised me too, but I think Ep VIII will address that.
I believe it's due to her heritage, and at some point we find out what that is. Ben is also very powerful (freezing the blaster bolt midair) due to his heritage - if I remember correctly, Leia was stronger with the force than Luke. I'm one of the few that's really excited to see where it goes with Kylo. I hope we get a redemption, and not just one on his deathbed or making a heroic sacrifice, we don't need to repeat Vader. I'd also love to see Rey struggle with or turn to the dark side - but not mirror Anakin becoming Vader either.
The whole cast of new leads (Rey, Finn, Poe, Kylo) bring diversity not just in race or gender, but character background that really opens up the storytelling potential. Anyone that's mad the lead role is again is female (not saying you are), you can 17 off with that. She had a strong performance in ep VII. Felicity Jones KILLED IT in Rogue One. We have plenty of badass male leads, I'd love to keep seeing badass female leads too.