OOoooh *warming up typing fingers* I'm so glad you asked.
So, Thor: Ragnarok has a lot of things going for it: humor, exciting action scenes, great visual design, spot-on music -- but all of those things are icing on the cake. The real excellence of the movie is that it's a powerful story of character perfectly delivered by a well-structured (brilliantly? yes, brilliantly is more accurate) plot.
At its heart, Ragnarok is the story of how Thor, who is heroic but believes that he is a hero for all the wrong reasons, develops into a real hero. His progress is mirrored by the three main supporting characters: Loki, Valkyrie, and Bruce Banner. Each one of them is also a partly evolved or partly lacking hero whose journey mirrors and sheds light on Thor's journey into heroism, and by the end, they have also developed into the most heroic version of themselves in complement to his development. His growth is highlighted particularly effectively through his repeated use of the phrase, "That's what heroes do."
That sentence is a single, but very telling instance of the use of structure and repetition to show the development of the plot and the characters. The plot itself is a textbook-perfect three act structure. In the first act, we see Thor and his world, learning about the conflicts he faces and his character. We see his skills, but also his willful ignorance and reliance on the use of brute force. Think of the way he lets Mjolnir smash up Dr. Strange's Sanctum and ignores the fact that Loki was trapped in freefall, essentially tortured, for the length of a couple of scenes: first act Thor wants to be a hero, but is also destructive and foolish. The first act comes to an abrupt and satisfying end with the appearance of Hel, who destroys Thor's hammer and flings him into a planet in the outer reaches of the galaxy.
The hammer -- of course the hammer is important: with his strength and his flowing golden hair, it's what he thinks makes him a hero. So to discover the deeper meaning of heroism, he has to be separated from it. Different characters point out the disconnect to him in a variety of ways throughouth the second and early third acts: Korg's reflection on his speech about the hammer; having his hair trimmed against his will; the way he gets shocked again and again, essentially having his own power turned against him; and his rivalry with the Hulk to be the "strongest Avenger".
I'll have to finish in another comment if you're interested. (hit the limit)