Someone asked whether it was okay to see Thor: Ragnarok without having seen the previous MCU movies. I haven’t seen it yet due to scheduling conflicts, but here’s my answer generally for the MCU: none of the previous movies are strictly necessary but they all build on each other and add specific parts of the plot. The Iron Man movies establish the creation of the Avengers and introduce SHIELD. The Captain America movies build on that with a lot of SHIELD history and the introduction of the Infinity Stones. The Thor movies largely suck but they are foundational for some of the big enemies, the space context, and the Infinity Stones. The Avengers movies tie the Earth heroes to the space context (leading into Infinity War) as well as set up the context for Captain America: Civil War (3), which covers some of the core conflicts and is sort of an Avengers-lite sequel. The Guardians of the Galaxy movies are fluffier but they also introduce a lot of the outer space context and lead into Infinity War. Doctor Strange and Ant-Man are fun throwaways that will probably have more implications later as the series gets deeper into the magic and quantum worlds. Watching the movies out of order will have some spoilers. Mostly this is some character or other mentioning something that happened in an earlier movie, but in some cases, it’s character relationships or the existence of characters, organizations, or objects at all.
[Edit: Someone else mentioned that Ragnarok has a lot of inside jokes you won’t get if you haven’t seen the other movies. I think that’s somewhat true of the others as well – there are definitely threads that weave the movies together, and that includes some of the running jokes.]
[Update: I have seen Thor: Ragnarok now, and Infinity War. The answer is no. Watch the previous movies first.]