Think about the legacy of Luke Skywalker. *****ZOMGSPOILERZOMGZ****** but if you want to avoid spoilers, you shouldn't be reading this anyway.
So Rian Johnson got to tell the entire story of Luke Skywalker, from the end of RoTJ until now. Why? Because Abrams spent the entire last movie building up to the moment on the island at the end of his film. The whole point of Episode 7 was "Find Luke Skywalker." Why? Because Luke was going to be the hero who saved the republic (? Why are the good guys rebels again after they won in RoTJ? How did the New Republic last only a single generation? These and a thousand other questions have yet to even be addressed, although I'll speculate here). So there's an entire movie's worth of build-up to the moment that Rey hands Luke a lightsaber in Episode 7. What happens? Luke takes the lightsaber, chucks it over his shoulder, and goes fishing.
Think about that for a minute. It was funny, sure, in a shocking way. But everything that had happened in episode 7 hung on that moment, and in that moment, Rian Johnson said: "I don't care about episode 7, I'm going to tell my own story." So there's the first break from continuity. Later, we find out that Luke went into Ben Solo's sleeping quarters with the intent to murder him. Ben not only defeats Luke in that moment but flees and turns fully to the dark side. Now let's think about this: In RoTJ, Luke walked, shackled and unarmed, into the Emperor's Throne Room on the Death Star, which he knew his friends were trying to destroy, just to save his father. There was a tiny glimmer of good in Darth Vader, the Sith Lord who had murdered literally millions of people, and Luke risked everything to save him.
But with Ben Solo (who was also family; he was Luke's nephew, the son of Luke's sister), he sneaks into his room at night and tries to murder him. Does that seem like the hero we remember from episodes 4, 5, and 6? Or is this a massive break in character from a character who is supposed to be significantly wiser and more powerful than he was in episode 6?
Then, he refuses to train Rey. He literally gives her three lessons, which end when she, literally, picks up some pebbles off the rock she's sitting on. Rey does some of her own lightsaber training on the island, sure, but she's clumsy.... she cuts the rock in half, rather than stopping her blade in the indentation.
So Luke is a coward and attempted murderer, who then runs away to die on an island in the middle of nowhere, while his friends (his sister, at the least) continues the fight. Han, by the way, turns out to be a deadbeat dad who abandons his family the moment things get difficult, but that's another post.
So, Luke decides to do something about it, right? After Rey leaves, Luke decides to go save the new rebellion (?) and shows up on the No-It's-Not-Hoth-Because-It's-Salt-Not-Snow planet to face Kylo. No, not really, he sends a force projection, and the effort of this literally kills him. Bam, end of Luke Skywalker.
He died a coward who refused to face even his own padawan, after trying to murder him in his sleep.
That's Luke Skywalker, the hero of millions for 30 years?
What's more, by doing this, Luke is single handedly responsible for the rise of the First Order (and I'm speculating here). If there had been a Jedi Order, it is unlikely that Snoke would have risen to power. Why? Because that would be exactly the thing Palpatine did, and the Jedi would have been on the lookout for it. They wouldn't have been so easy to fool the second time. So Luke not only fails to prevent the ascension of Snoke, but also fails to prevent the ascension of Kylo Ren, who undoutably aids the First Order in some very significant ways, as he is very easily able to appoint himself supreme leader of the First Order on the death of Snoke.
While Luke was fishing and drinking blue milk, instead of tending to his duties as the only remaining Jedi, the galaxy fell apart.
Imagine if Superman got shot by a street thug, and the bullet pierced his skin and lodged in his lung. Not a kryptonite bullet or anything, just a regular guy.
Imagine if Batman lost a fight to a yellow belt in Karate class. He didn't throw it, he just genuinely got his butt kicked.
Imagine if a short fat bald guy like me beat the Flash in a footrace. No speed force, just me running my 38 second 100-meter dash like the chump I am, and I outran the Flash...
What would we say? We'd be upset. We'd call it bad writing. We'd hope it was a dream sequence.
We'd say it wasn't real.
#NotMyLuke
No Jedi ever wins a fair lightsaber battle against a fully trained Sith in any of the movies until Return of the Jedi, where Luke beats Vader. 
In Revenge of the Sith, when Palpatine (Darth Sidious) faces FIVE JEDI MASTERS, he kills four of them before they are even ready to fight him. The fifth, Windu, APPEARS to defeat Palpatine, but Palpatine was feigning weakness to draw Anakin to the dark side. Because as soon as Anakin crosses the point of no return, Palpatine unleashes "UNLIMITED POWER!!"
