Avengers: Infinity War

Essential, and it is the payoff for ten years of films. It is also the least watchable cold of anything here: there is no introduction to anybody, the film assumes you know roughly twenty characters, and it opens on a massacre of people you met in another film.

The structural decision that makes it work is giving the story to the villain. Thanos is the protagonist: he has an objective, a plan, obstacles and a cost, and the film is organised around his journey while the heroes react. That is why it has momentum where an ensemble this size should have none.

Josh Brolin's performance is the reason the conceit holds. The film commits to Thanos believing he is merciful, and the Vormir sequence, in which he has to give up the one thing he loves and does, is the moment it stops being a plan and becomes a conviction. Whether his economics make sense is beside the point; he believes it.

The ending was the most discussed in modern blockbuster cinema and depends entirely on the audience's investment in characters built elsewhere. Endgame follows directly and the two are one story. Watch them together if you can.