Almost right off the bat, Rian Johnson's film was upsetting a section of Star Wars fans. We'd waited two years to see how he'd react to Rey turning up on Ahch-To and handing him back his lightsaber, and his response is to simply throw it away and walk off? What?!
One thing everyone can agree on is that it's a clear marker that this film isn't going to play to expectations, nor just be a retread of The Empire Strikes Back. A lot of fans, however, have taken this as a sign of disrespect from Johnson for Luke, the franchise, and its fans; a massive "f**k you!"
Instead, this serves as an early indicator of not just who Luke Skywalker is now, but how haunted he is by the past. This is a Luke who has not only exiled himself from all of his friends, but - despite being one of the most powerful Jedi to ever live - has managed to completely close himself off from the Force, because of his fear he'll only do more damage.
And then some random girl turns up and gives him a relic directly connected to the Force, the Jedi, and his past - what else is he going to do? Accepting the saber means you don't set up Luke's arc, or have to go down a different route that wouldn't be true to the story, and there's no other rejection as immediately dramatic as him throwing it away.
One of the many complaints about the film is how Johnson does away with things set up by Abrams. And yet, the reason he took on the job of Episode VII was because of one big question: "Who is Luke Skywalker?" Despite that, Abrams never gives us an answer in The Force Awakens, but Johnson gives us a great one in this movie, within the parameters of what was feasible after The Force Awakens, and this is simply the start of it.