The Marvel movies have always been very light-hearted and fun, leaning heavily on humor and wit to keep the audience's attention during the slow dialogue bits. Thor: Ragnarok seems to take things to a new level though -- at least, outside of the Guardians of the Galaxy movies. Ragnarok comes off as almost a full-blown comedy. It's good. It works well. I just hope that this doesn't become a new de facto template for future Marvel movies, as it would eventually run itself very dry.
That being said, the Marvel films have definitely shown signs of growth after Avengers: Age of Ultron. The plot doesn't revolve around a magic MacGuffin, and it's not even really a revenge story. The bad guy just wants to conquer Asgard because she's an ambitious bitch who wants power. There's a little bit of a vengeance angle, as she's obviously mad at Odin and Asgard for imprisoning her. But Odin's dead before she even shows up, so she basically just shows up and says "kneel before me or be destroyed." Hela is kind of bland. I wish they'd done more with the Planet Hulk stuff instead -- maybe even making Hulk be the bad guy?
I also initially struggled to find any sort of core, unifying theme, and walked out of the movie not quite sure what it was supposed to have been about. The overarching theme seems to be that Thor doesn't need the hammer to be powerful, but isn't that just retreading the core lesson that he learned in the first movie? Besides, the whole "the power was in you all along" thing only comes up at one point mid-way through the movie, and then Anthony Hopkins' Odin shows up at the very end to just tell Thor that he doesn't need the hammer. It felt like a bit of a copout.
Ragnarok has no compunctions about shaking up the status quo.
But I don't think the Dumbo storyline is actually the point here. I think the point is the movie's fatalistic (yet still, somehow, upbeat) ending. Despite the tongue-in-cheek, comical tone, this movie does nothing if not completely disregard that status quo. True to the movie's namesake, the end of the world actually does happen this time around! Asgard (along with the Rainbow Bridge) is destroyed, Odin is dead, The Asgardian army has been massacred, Mjolnir is destroyed, Bruce Banner is [supposedly] irreversibly transformed into the Hulk, and so on.
Thor makes recurring jokes about Loki constantly (and predictably) betraying him, and yet Loki keeps seeming to slip closer and closer to actually becoming a good guy. One of the secondary characters even jokes that the foundation of Asgard still exists, and so they can rebuild, only to have the entire plane of Asgard literally explode as he ends that sentence. Nevermind.
It's a fun, colorful ride all the way through to the end.
The end of the movie is kind of a downer, but the ride to get there is a heck of a lot of fun. The movie is very vibrant, colorful, energetic, and full of an almost overabundance of humor. There's no less than three separate Dark Souls boss fights. Hesmworth and Hiddleston are as charismatic as ever, Hulk is a riot (even though the writer's totally missed the opportunity for Hulk to shout "bad dog" as he's beating up Hela's wolf), Taika Waititi is a comedic standout as the rock creature Korg, and Jeff Goldblum is ... well, he's Jeff Goldblum.