I've thought about it and

Thor: Ragnarok was bad. It was fun, but it was also bad. MCU crossover movies have this inherent problem of being a bunch of stapled-together, fan service-y pastiches, so the first 20 to 30 minutes were wasted on that. The tension between "Loki as vicious cutthroat traitor" and "Thor and Loki Buddy Cop" means that neither motivation is convincing. And the final climax was obvious from the point that Thor brought Surtr's skull back.