For me it was the transcendence of Luke. Basically Luke retreats from the world, totally blowing it and missing the point, paralyzed by over analyzing what consequence every action he takes could have in the future. Yoda comes back to impart one last lesson, that his weakness is the same, always thinking about the future and not enough focus on the moment. That moment is actually the climax of the movie (though it didn’t hit as hard as it should have). It free’s Luke to reengage with the world and make his last stand, completing his story arc from “A New Hope” culminating with his absorption into the force.
In this way I agree with this Tech Crunch article:
The Last Jedi should be the last Star Wars film
The story of Luke and Han is concluded. The lesson is there is always balance “they shoot you up this time, you shoot them up next time” as benicio del toro’s character puts it. Life is existential futility and we all do the best we can, and just maybe inspire the next generation to do a little better (cut to kind waving broomstick like a light saber and fade out)… but you know, more movies to make.
Ironically this movie was filmed before the last election, but it was definitely riffing on a lot of those themes.
Star Wars: The Last Jedi Offers the Harsh Condemnation of Mansplaining We Need in 2017:
Frankly, in every other Star Wars movie the heroes go off half cocked without much of a plan and it magically worked out. In this one Poe does that twice with disastrous results, the first with the bombers, the second by sending Finn and Rose on that mission which basically alerts the First Order to the escape plan. I thought that was a nice twist, but again, maybe didn’t home because there were a lot of themes going on.
As far as Snoke not reading Kylo’s mind… he was reading it. If you think back again, every word Snoke said paralleled what was going on with Rey’s lightsaber. Star Wars has a pretty good track record for killing off villains without much ceremony and without much backstory. We didn’t know much about the Emperor until the prequels… and with all that power Vader just picks him up and throws him over the railing? Similar with Data Mal (oh crap, did I just reference the prequels twice?)… Jaba gets choked out pretty quick. Boba Fett, need I say more 
Another interesting article on making heroism more inclusive, the combination of many small deeds vs big acts: