But... it was Kylo Ren that turned on the new order. That was pretty clear to me. He was seduced by Snoke, sure, but but it was him that did the killing.
I also enjoyed the utility of the hilt being proven.
Funny how one word can change the course of a movie. I (mis)heard Han say 'He should have gone to Luke', which lead me to believe that he hadn't - that they'd sent him away, and that the one who turned on the new order was Snoke, who then formed the Knights of Ren and recruited Ben, who has not yet completed his training and his fall to the Dark Side (until the bridge incident in this movie). I thought it was a great plot twist and opened a lot of story options for the future.
Sadly Han said "He shouldn't have gone to Luke" - which means that a whiny, emo, half trained apprentice betrayed his uncle and wiped out all the other acolytes yet still felt the pull of the light for some reason (so much for Yoda). It weakens every character involved - the unseen other acolytes, Luke (you... probably shouldn't let your nephew who just slaughtered everything you were working on go wander off), Luke again (oh, and you missed this Dark Side user named Snoke. Nice going.), Luke a third time (seriously, maybe you should have noticed something was off about your nephew), Leia and Han (yep, he just killed a bunch of people and went and joined the empire remnants - be casual when you say 'I saw our son')...
I enjoyed it more with the misunderstanding.
Luke better have a really, really, really good reason for becoming a hermit instead of confronting Jacen - er - Ben. Obi Wan did because there was nothing he could do - both Palpatine and Vader were stronger than he was, were together by the time he realized Anakin had survived, and he needed to keep an eye on Luke as he grew - probably both to make sure the Empire didn't come looking and make sure that Luke didn't follow in his father's footsteps. For the record, I didn't give Yoda a pass on becoming a hermit, either.
But that is what sequels are for, after all. If this trilogy mirrors the first trilogy, as they've stated, and the second mirrors Empire as closely as Awakens mirrored Hope then Luke will have plenty of time to explain things as he trains Rey - until she runs off half trained because Finn and Poe get cornered by Kylo somewhere and it is revealed that he is her brother (or cousin).