Unless you’re a total fanboy you’re likely to need an annotated roster to understand much of “The Avengers: Infinity War,” a long, very expensive mash-up of all the threads of the Marvel superhero universe in one gigantic, gaudy, barely digestible package. That will be a distinct disadvantage for those who haven’t watched the previous installments in this long-running, incredibly successful, mega-franchise over and over again, or—heaven forbid!—skipped some of them either out of distaste or sheer exhaustion.

But even those well versed in the earlier pictures may be less than enthused by this enormous episode: overstuffed but underwhelming, “Infinity War” is burdened with too many characters, too many battles, and an ending that is meant to shock but is obviously a cheap trick bound to be reversed when the sequel comes out next year.

The jumping-off point for the script by Christopher Markus and Stephen McFeely is clearly the 1991 comic-book miniseries “Infinity Gauntlet.” In this telling the villain Thanos (here played by James Brolin, who looks like Ron Perlman encased in rubber and gives a monotonous vocal performance) is on a mission to collect the six colored infinity stones (governing Mind, Soul, Time, Power, Space and Reality) that date from the Big Bang. His purpose has a crazy idealism to it. Certain that the universe is overpopulated, he plans to use the stones to order the random annihilation of half the life forms in it. But to do that he needs all six, and so after taking one being guarded by a powerless Thor (Chris Hemsworth), he goes after the another in the hands of Dr. Strange (Benedict Cumberbatch) on earth. He’s accompanied by his cadaverous enforcer Ebony Maw (Tom Vaughan-Lawlor), a cool customer who’s actually creepier than Thanos, who spirits Strange to his ship for an extended torture session.

That sets off a jumble of interlinked plot threads as the Avengers, the Guardians of the Galaxy and assorted other heroes, including the Black Panther (Chadwick Boseman) and his Wakandan countrymen and women, are divided up into contingents to rescue Strange and prevent Thanos from getting all the stones, another of which is lodged in the forehead of Vision (Paul Bettany). Multiple fights and escapes ensue.

It would be as tedious to outline the course of this here-and-there struggle as it becomes, over the course of the movie’s two-and-a-half hours , to keep everything that’s going on straight. Suffice it to say that in addition to Thor, Strange and Panther, among the others who take part are Iron Man (Robert Downey, Jr.), Captain America (Chris Evans), the Hulk (Mark Ruffalo), Black Widow (Scarlett Johansson), Spider-Man (Tom Holland), Scarlet Witch (Elizabeth Olsen), War Machine (Don Cheadle), Falcon (Anthony Mackie), White Wolf/Winter Soldier (Sebastian Stan), Loki (Tom Hiddleston), Star-Lord (Chris Pratt), Drax (Dave Bautista), Gamora (Zoe Saldana), Rocket (Bradley Cooper), Groot (Vin Diesel), Mantis (Pom Klementieff), Okoye (Danai Gurira), M’Baku (Winston Duke) and Shuri (Letitia Wright). And that’s just the tip of the iceberg. Other familiar characters also appear, like Nebula (Karen Gillan), Heimdall (Idris Elba), The Collector (Benicio del Toro) and Pepper Potts (Gwyneth Paltrow).

If that sounds like an awful lot of folks to do justice to in a single movie, even one of epic length, it is. A few, like The Collector, appear so briefly that if you blink or go out for a refill on the popcorn you’ll miss them. But even some of the “stars” receive short shrift. The result is a movie that seems like a superhero version of the old all-star revues that MGM used to put out periodically in the thirties and forties, featuring their stable of contract performers in brief turns. But though none of the actors come off particularly well, they all go through their paces with their usual professionalism, and ably deliver the juvenile jokey banter that passes for dialogue in such flicks and provides brief pauses between all the interminable CGI battle scenes.

It may be noted, without introducing specific spoilers, that there are deaths in “Infinity War,” some of important characters. But it has to be recalled that in this genre, death is not necessarily a permanent condition. Indeed, more often than not, it isn’t.

Technically the picture exudes the efficiency that Marvel has achieved over the course of this long run of product. True, there’s an assembly-line quality to the result, but one can’t dispute that Anthony and Joe Russo’s direction and the editing by Jeffrey Ford and Matthew Schmidt keep things moving, that Trent Opaloch’s widescreen cinematography is fine, and that the army of special effects craftsmen perform yeoman service. From Alan Silvestri’s score, it sounds as if he has been studying John Williams’ “Star Wars” music; brass blasts introduce virtually every transition from scene to scene—and there seem to be hundreds of them.

Of course, no criticism one might put forward about “Infinity War” will deter people from going to it in droves; following the ever-expanding Marvel Universe has become less a choice than a habit. The movie is going to be a huge hit, and the crowds will even stay through the long closing credits to see the single additional scene at their close.

If you’re interested in what might follow in next year’s sequel, you might want to check the two Marvel comic mini-series that followed “Gauntlet” for clues: “Infinity War” (1992) and “Infinity Crusade” (1993).