Star Wars: The Last Jedi Trailer Reactions - 8 Ups & 2 Downs
4. Kylo Ren

When he cut down his father in The Force Awakens, Kylo Ren could have simply blossomed into the full-blown villain Snoke seems to want him to be. He could have symbolically cast off his past at that moment and become Kylo Ren fully, but it wouldn't have been as intriguing to watch his arc from that point.
It is far more interesting to focus on Ren as a more complex, ambiguous figure who hasn't yet arrived at his final destination and who - like his grandfather - could be turned back to the Light side at any moment. He's better when he's haunted by the contradiction of what he wants to be and what he was, and the suggestion that he will fail to kill his mother when instructed to throws a giant spanner in the works.
This trailer is very good to Kylo Ren, showcasing Adam Driver's excellent performance and hinting that he and Rey have easily the most interesting arcs in there. But then you should already have known that.