Watching the last "Avengers: Infinity War" trailer, two things are clear. First, the Marvel Cinematic Universe has a lot of heroes in it. And second, more heroes doesn't necessarily mean "better films."

To be fair, the trailer is a triumph of coordination. After 10 years and 18 films in the Marvel Cinematic Universe (MCU), it's not easy to pack every hero in the franchise into a single ad. But Marvel goes for it. By my unscientific count, the trailer includes (more or less in order) Hulk, Black Widow, Iron Patriot, Dr. Strange, Gamora, Iron Man, Spider-Man, Scarlet Witch, Vision, Captain America, Black Panther, Okoye, Shuri, Star-Lord, Drax, Rocket Raccoon, Thor, Groot and Loki. The trailer misses some people — there’s no Valkyrie, no Ant-Man, no Hawkeye, no Nick Fury. Still, that's 19 heroes, not counting the big purple villain Thanos himself. Not bad for two minutes and 18 seconds.

But impressive choreography aside, “Infinity War” as a film looks underwhelming. Even at just a couple minutes, the plot drags; the film looks mired in exposition, default profound movie music, and carnage for the sake of carnage. When you've got so many people to position, you don't have a lot of room to tell a story — which is a problem both for this trailer, and for the MCU as a whole.

Get the think newsletter. This site is protected by recaptcha

Superhero crossovers have been central to Marvel since Stan Lee, Jack Kirby and Steve Ditko created classic heroes like Spider-Man, the Fantastic Four and the Avengers in the 1960s. Marvel didn't invent the idea of having superheroes team up; the Justice Society of America was up and running at DC Comics 20 years earlier. But the Marvel bullpen embraced and explored the idea of a shared universe in new ways. They had Thor pop up in a cameo in a Dr. Strange story, or the Hulk fight the Thing — because what fan doesn't want to see the Hulk fight the Thing?

Marvel comics were fun in part because you could open any title anywhere and stumble on a genius scientist, a Sorceror Supreme, a god or a big green monster. The Marvel Universe was a place of familiar wonders — a gigantic clubhouse you entered to meet old weird friends, and watch them blast each other.

The MCU has, improbably and brilliantly, recreated the comics crossover experience in the much more expensive and logistically challenging medium of film. Coordinating storylines, not to mention actors’ schedules, over multiple films, each of which takes years to conceive and produce, is a remarkable technical achievement. To see how remarkable, you need only to look at the struggles of DC's copycat universe, or the abortive, embarrassing effort to launch a Universal Monster cycle of films.

Marvel comics were fun in part because you could open any title anywhere and stumble on a genius scientist, a god or a big green monster.

At its best, Marvel has used its shared universe to highlight unexpected chemistry between unexpected actors and characters. Taika Waititi turned the Thor/Hulk relationship into a delightful hate-and-lovefest in "Thor: Ragnarok," Robert Downey, Jr.'s fast-talking cynicism provided a surprisingly ideal foil to Tom Holland's naïve everykid Spider-Man in "Spider-Man: Homecoming." When it successfully creates such juxtapositions, the sprawling film universe does seem like it's more than the sum of its parts.

But shared universes have their downsides too. Films like "Age of Ultron" and "Captain America: Civil War" started to buckle under the weight of their proliferating superfolks. Characterization starts to get squished and stretched like taffy to fit the increasingly convoluted demands of the plot. The vengeful T'Challa (Chadwick Boseman) wheeled out to provide additional drama in "Captain America: Civil War" is a far cry from the thoughtful and merciful figure we get to know fully in "Black Panther." And for that matter, why do Ant-Man, Iron Patriot, or any of the secondary heroes in "Civil War" choose the sides they choose? They function more as action figures than characters — lined up against each other because the script calls for a big fight, and these are the pieces directors and writers have on hand.

The biggest problem with the MCU is plot-based. When all the movies exist in the same universe, there are strict limits on where and how far each film can go.

The biggest problem with the MCU, though, is plot-based. When all the movies exist in the same universe, there are strict limits on where and how far each film can go. Superhero fans like to boast that you can tell any kind of story as a superhero story, and it's true that the genre can be surprisingly flexible. But that flexibility is most in evidence in films that exist outside the Marvel universe. The bleak melancholy of "Logan" is possible in part because the X-Men franchise, owned by Fox, isn't connected to the MCU films (though it may be in the future thanks to the Disney-Fox merger.) And even "Logan's" use of the superhero genre is tame compared to non-Marvel films, such as the bizarre, deliberately anti-climactic anime TV series "One-Punch Man," or the scruffy, horror found-footage vibe of "Chronicle" (2012).

The pressure to fit into a world they didn't make puts limits on what filmmakers can do. Director Edgar Wright's presumably weirder, sillier "Ant-Man" got rejiggered when Wright was replaced by Peyton Reed to make sure the movie fit into the rest of the Marvel Universe. "Black Panther's" conclusion promises a transformational, Afro-futurist world that future films can't really explore. Rather than thinking through the implications of a world transformed by Wakandan tech, we have to rush off to fight Thanos. Tony Stark's inventions haven't notably changed the everyday lives of Marvel universe inhabitants; Wakanda's won't either. The MCU has to stay the MCU — which is to say, it's a place that looks like our world, but with lots of superfolk running around.

Obviously, given the box office success of franchises like the Avengers, it seems most movie audiences are happy with the way the films generally turn out. Getting to see Captain America fight Black Panther, or Iron Man trade quips with Star-Lord remains an upside for fans. Marvel’s universe promises to show all your favorite heroes in one place. The "Infinity War" trailer fulfills that promise, but at the cost, perhaps, of other accomplishments.

Noah Berlatsky is a freelance writer. He edits the online comics-and-culture website The Hooded Utilitarian and is the author of the book "Wonder Woman: Bondage and Feminism in the Marston/Peter Comics, 1941-1948."

CORRECTION (March 20, 2018, 4:45 p.m. ET): An earlier version of this article misidentified one of the superheroes in the new "Avengers: Infinity War" trailer. The trailer included War Machine, but not Iron Patriot.