His head is a different size. Kylo Ren was unmasked to see Adam Drivers face(a lot).
There Finn is fighting Kylo Ren in the dark snowy forest. In the whole story, it talks about them fighting in that forest but Kylo Ren has his mask off. Why would Luke Skywalker want to be evil just like his father. And Kylo Ren idolizes Darth Vader like he did good. Kylo Ren is a knight of Ren and why would Luke ever be a knight of Ren.
Also other stuff.
Why is Finn not wanting to be a storm trooper? Maybe He realizes that they do wrong. We will have to find out in the movie.
Who is the voice that Rey is taking to? Some think it is General Leia. Notice how I said general. She becomes general of the rebels. Well actually that voice is Maz Kanata.
She might be the one who hands that,"person," Anakin's lightsaber. She is played by Lupita Nyong'o.
Also as concept art, Maz Kanata is with a lightsaber crystal so maybe.