Here be spoilers.
Ever since the prequels wound up being at least a little bit inept, large swatches of Star Wars fandom have delighted in acting like they know more about the franchise than the people actually writing the stories within it. George Lucas might have thought that it was a cool idea to start his trilogy about the emotional downfall of one of the most iconic representations of evil and villainy in all of storytelling with a film centered around a complicated trade dispute, but the guy isn't a complete idiot. He was fully aware that he was telling the story of the Jedi failure, but fans can have a tendency to talk about this as though Lucas didn't realize exactly what he was doing. Again — Lucas might have misfired on a lot of ideas when it comes to the prequels, but the subtext of the Jedi Order's role in the birth of Darth Vader wasn't one of them.
Now that Star Wars has been soft-rebooted, so to speak, it's open to a new narrative paradigm that wasn't really possible before. Open for the first time to storytellers with a bit of distance from its initial conception and execution, the Star Wars franchise finds itself with some unprecedented potential for meta-commentary. Neither the prequels nor the original trilogy were capable of commenting on the legacy they were actively becoming part of, but a 30-year remove puts this new generation of storytellers in a very unique position: Star Wars stories can now be told in a way that thematically and sub-textually comments not only on the very franchise they are a part of, but on the extended legacy of that franchise, its cultural impacts, the nature of its relationship with its fans, and so on. For the first time, Star Wars movies can be about the cultural institution that is Star Wars movies.
Now I'm as staunch an Abrams apologist as they come, but at this point it's more or less apparent that JJ isn't interested in taking any real risks with this new potential. His is a deep love of homage, and thinking back to a story about his on-set mantra being "Is it delightful?" during the production of The Force Awakens points to a clear difference in his storytelling goals when compared with Rian Johnson's work on The Last Jedi. If Abrams' aim is to delight, Johnson's is to pick apart all that shit that you've been delighted by for the last thirty-some-odd years, thematically shoulder his way right past all your easy nostalgia buttons, and demand that you ask yourself why you were so delighted by all of it in the first place.
And all The Last Jedi needed to be was a rip-roaring Star Wars flick. Delightful would have been enough! Hell, it was fine for Force Awakens and Rogue One, so why not this one? It just wasn't enough for Rian Johnson. He seems to have set his goals a little higher, and his resultant work has elevated the franchise to heights it hasn't reached since Empire Strikes Back. Through a series of storytelling choices that elicit a deep understanding of the Star Wars franchise as well as its fandom's complex relationship with it, The Last Jedi doesn't just accomplish things that Star Wars had never done before, it accomplishes things that weren't even possible for Star Wars to do before in the first place.
The Jedi Failure
The Last Jedi made it no secret that Luke Skywalker has grown sick and tired of everyone's favorite order of magical laser-sword space-knights. Hell, they put it right there in the trailer. Luke is not down with the Jedi anymore, and he wants them to be donezo. Then, at a certain point, Luke explains to Rey that despite all the myth-making and galactic hero-worship, "The legacy of Jedi is failure...hypocrisy, hubris." He even goes so far as to point out that the Jedi basically let Palpatine rise to power when they were at their strongest. All things that any Star Wars fans will recognize as having come out of the mouths of people who think they understand Star Wars better than Lucas does.
To a degree, this is understandable: While the Jedi failure was clearly and intentionally played out in the action of the prequel films, its interpretation is more or less implicit, and has never — for lack of a better term — been "made canon" in a diegetic sense. Fans have been quick to assume that, since the Jedi have been treated with reverence by most all characters within the Star Wars universe itself, their failure was not rooted in Lucas' authorial intent. Thing is, most Star Wars stories don't center on characters who have actually been through all of the core films thus far. Given The Last Jedi's temporal setting, this makes Old Luke one of the only characters in the Star Wars universe who can actually offer up an authoritative analysis on the events of both the prequels and the original trilogy.
That analysis? To sharply rebuke the Galactic Good Guys for having been a failure and condemn them for having been driven by hubris and hypocrisy, essentially calling for an end to their existence.
But by brilliantly deciding to make failure the thematic throughline of The Last Jedi, Rian Johnson canonizes the Jedi failure as being recognized thusly in the most poignant way possible, elevating it to a vital teaching role within the hero's journey. At the same time, the Jedi are humanized. De-deified. The Last Jedi shows us that the Jedi have always had their hearts in the right place, even though they sometimes fuck up the execution. At the end of the day, they were fallible. They had to learn from their mistakes and miscalculations, just like us regular, non-magic folk. Even Luke comes to learn that his criticisms don't need to be quite as sharp as they had been, because the Jedi were never supposed to be regarded as infallible gods in the first place. They were capable of misjudgment just like anyone else, and their true power lied in their ability to learn from these failures and integrate them into their journeys. So sayeth Yoda, in one of the film's most thematically important moments. The Jedi weren't perfect Chosen People...they were People.
The Rey of it all
And so it turns out that the Skywalker Saga isn't just about the Skywalkers. Up to now, it's been easy enough to interpret the core Star Wars saga as being about a single family around which the fate of the struggle between good and evil within the galaxy seems to hang. In The Last Jedi, however, Rian Johnson thumbs his nose directly at this idea, tossing all that destiny, chosen one nonsense right over his shoulder (remind you of anyone?).
Think about how intentional this decision must have been. There's no way Johnson wasn't acutely aware of the conversation surrounding Rey's origins; remember that this is one of the first Star Wars films produced in a way that actually allows for reflexive commentary. This type of storytelling wasn't even possible until now, and the reveal that Rey comes from outside the Skywalker lineage has implications that ripple back to the very DNA of the original trilogy itself.
The Last Jedi firmly and confidently asserts that Rey doesn't have to be the progeny of someone previously-established as being "special" in order to play a vital role in the struggle for good and evil. Rey isn't a hero because she was born a hero, she's a hero because she decided to use her gifts and abilities to actively become one. She doesn't have to be the secret spawn of some major player on the galactic stage the way Luke was. It's enough that she's someone who has the ability to make a difference, and is determined to do so in a positive way.
As such, Rey's call to adventure is entirely her own. It doesn't come attached to the legacy of some important dude who came before her; it's borne out of her own agency, and of her decision to use her gifts for good.
The Hero's Journey
Above all else, Rian Johnson remembered that Star Wars is a telling of the Hero's Journey. Lucas was famously fascinated with Campbell's contributions to the field of comparative mythology, and it's no secret that The Hero with a Thousand Faces informed a lot of the Star Wars blueprint. The Last Jedi has no shortage of heroes that emerge over the course of its movie-and-a-half runtime, but what's incredible about Johnson's screenplay is how much thematic depth emerges from a film that allows itself the time to comment on how those journeys actually start.
In its retroactive illumination of how Rey's hero's journey started, The Last Jedi strengthens itself with a valuable thematic insight on the very nature of Campbell's monomyth (and something a lot of ancillary Star Wars material seems to have forgotten) — heroism is universal. It's for everyone. The Hero of a Thousand Faces is fundamentally about the universality of the hero's journey, and The Last Jedi makes this idea literal by depicting the Rebellion's contagious spark as it makes its way across the galaxy.
We are all our own heroes, each of us on our own journeys. Background doesn't matter. Luke and Rey both stared up at the sky towards the start of their respective journeys with the same wistful look on their faces, a gesture that speaks to a truly universal desire to have our complex, complicated lives pared down to something as elemental and simple as "good versus evil."
And all this thematic legwork is what makes the oft-derided Canto Bight sequence not just an absolutely indispensable part of The Last Jedi, but also one of the sequences that clarifies Rian Johnson's deep understanding of the Star Wars mythos.
First of all, consider the fact that the Canto Bight mission fails. Finn and Rose touch down with the goal of finding someone who can help the Rebellion, and they fail. They find someone who does help them, but it's not exactly the help that they wanted, and it's not exactly delivered in the way they expected. Just like Rey's mission to find Luke and bring him back, their Hail Mary play doesn't go exactly as planned, showing us that failure is always part of the journey. This sequence also zooms out on the Star Wars universe a bit, showing us a larger context for and the impact of the galactic conflict we've been following along all these years. It's not just the Rebels who suffer at the hands of the Empire: both sides are engaged in a massive, churning war machine, and the Canto Bight sequence offers a valuable look at those left in its wake.
Most importantly, though? This sequence sows the seeds for another hero's journey. Remember, Luke was a conflict bystander who once stood in a shitty place and looked up at the sky wishing he could be part of something bigger. The Last Jedi ends with a poignant shot (perhaps the most meaningfully significant frame in the entire franchise) that shows a slave boy, having recently been inspired by Rose and her Rebels, looking up at the sky and holding his broomstick so it looks like a lightsaber.
The spark spreads. Yet another hero's journey begins. And not because of special parents, but because someone helped. The Rebel Alliance has started the fire of yet another Hero's Journey somewhere in the galaxy...even though the Canto Bight mission was technically a failure. It's all part of the journey.