1) At the end of the last Thor movie, called Thor: Dark World, Loki was in charge of Asgard. The fact that the god of mischief is sitting on the throne of Odin leads to a lot of laughs. I think I'm going to miss Tom Hiddleston, who may never again reprise his role as the famous trickster. However, Disney does have the ability to back up a truck load of cash....
2) "Ragnarok" is a term that's used in the Marvel comics to signify a reset of Asgard. In the comic books, it's happened a few times already. Each time the Asgardians get reborn and everything goes back to normal. This movie is a bit different, because it mashes two storylines together: Planet Hulk and Ragnarok. It ends up being a fantastic mashup because it's fun seeing Hulk and Thor together. And let's face it...Hulk is only good when he has amazing things to tear into and smash. Him being in a solo movie by himself is kinda boring because he needs a villain powerful enough to stand up to his fists.
Okay, so here are my assorted musings (and I don't think any of these are spoilers):
1) Cate Blanchett as Hela, the goddess of death, is a huge win. I want more Hela.
2) Loki and Thor have incredible chemistry. You can tell their characters love each other, and when they fight together it's kinda magical. It's a shame that Loki's always going to stab Thor in the back when he least expects it.
3) The script writing is smart smart smart. Every moment is either a laugh out loud moment or just witty banter.
4) It sets up the Avengers: Infinity War really well. You should stay for both stingers. The last one with Jeff Goldblum is hilarious (much like the rest of the film).
Go see Thor: Ragnarok guys! Seriously.