(Yes, that's what it's officially called in the UK.)
One newspaper reviewer referred to this as a Greatest Hits compilation of all the preceding Marvel movies from the same studio, which is a little unfair to the film, but not entirely unfair to the Avengers the comic-book hero team, whose only reason for existing is really to be a bunch of popular characters, all together! The Fantastic Four are a family; the X-Men are a shared experience of prejudice, but the Avengers are ... Earth's Mightiest Heroes. Except when the rotating membership list takes the mightiest ones out and cycles some second-stringers in.
But the movie, starting fresh, was able to include a goodly collection of mighty fan favourites, while quietly avoiding the comics-founder-member but probably-nigh-unfilmable (on grounds of silliness) Ant Man and Wasp. Then it added Hawkeye, to up the human-identification and cool-gadgets factors, and Black Widow, to provide eye candy and avoid, as Joss Whedon apparently had to point out to the studio, having the whole thing look like a gay cruise. I'm not sure that Scarlett Johansson in a black catsuit lowered the testosterone level of the movie very far, but she probably ensured that Whedon could be brought aboard, which was the important thing.
("Yes, okay Joss, you can reenact the Buffy-Angel thing with Black Widow and Hawkeye.")
Because, if we're going to have compendiums of good bits and character grace
notes and cliches from other movies, some in completely different
genres, some of them cliches so new that Michael Bay has barely finished
inventing them, then this the way it should be done. Whedon seems to be the Hollywood-acceptable name best suited to constructing these superlatively choreographed action scenes and intervening character angst-fests. Heck, he even manages to construct a justification of sorts for the team name, which is more than Marvel have ever managed in fifty years of publishing the title. (The fact that personal vengeance, while much beloved of Hollywood and Hong Kong action movies, is a rather sleazy motive for heroes, is neither here nor there.) And there's little arguing with the audience numbers, which say that we are going to get more of this sort of thing, whatever.
Meanwhile, Tom Hiddleston, basically unknown in Hollywood before Kenneth Branagh spotted his potential for Thor, makes sure of his options for a very profitable secondary career playing Hollywood villains with English accents. In this movie, Loki gets to engage in more spring-heeled physical violence than I ever remember him bothering with in the comics - where he's a generic smug super-mage - and more blue-eyed spitting villainy, and Hiddleston strolls it. Whatever happens with Marvel comics-based movies, I think that we have a worthy successor to Alan Rickman. Which I guess is a win.