While the $80 million four-day gross for X-Men: Apocalypse fell essentially in line with the studio's expectations heading into Memorial Day weekend, it's still being looked at as something of a disappointment by analysts, who cite the $110 million four-day opening for the last film in the franchise-- 2014's Days of Future Past -- in making their case. As Box Office Guru founder Gitesh Pandya put it, "Looking at tickets sold, its opening weekend ranks 7th out of the 9 X-Men universe films."

Which raises the question: why did the biggest, most character-rich X-Men movie yet fall so short of its predecessor? We reached out to box office analysts to weigh in, and they offered up three big reasons why Apocalypse fell short.

1. It garnered far worse reviews than the two previous films in the franchise.

Finishing with a lackluster 48% average on Rotten Tomatoes, Apocalypse came up far short of the two previous X-Men films with critics (First Class logged an 87% "Fresh" rating while Days of Future Past came in at an even better 91%), and that likely made a difference with audiences in the social media age, where insta-feedback is the name of the game.

"Movie reviews historically didn't damage the opening weekend of major titles. That was in the days before social media, though," said Box Office Prophets founder David Mumpower. "Now that word spreads so rapidly, in any instance where a blockbuster suffers through some savage reviews, the studio has cause for concern. The under-30 crowd, the bread and butter of movie box office, are savvier than ever. If their friends say something is terrible, they'll spend their money on something else."

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2. It offered too much of the same.

"If you look at superhero films that have done unexpectedly well recently...like Deadpool or Guardians of the Galaxy...the studio goes for something a little more outside the box," said The Numbers founder Bruce Nash. "And I think that the mistake that was made with Apocalypse was to try to be too much like a Marvel Avengers movie."

In Nash's view, the genre's long history of oversized stakes may be part of the problem; like so many superhero films before it, Apocalypse centers on a villainous plot with world-ending potential. "I don't think [it's] the fault of the film, I think it's just that people have seen the world under threat one too many times, and actually when you think about Captain America[: Civil War], which was a movie that didn't play that theme again, that actually worked a little bit better for audiences," he said. "You can only see so may aliens invading Manhattan before you go, 'okay, well, I'll look for something else to watch.'"

3. The trailer didn't adequately justify the movie's existence.

"The trailers always felt a bit muddled, as if nobody really had a strong feel for the purpose of it," said Mumpower. "They simply wanted to earn more money with an X-Men release rather than put a lot of thought into the purpose of the release. It's the most crippling mistake a studio can make with a sequel, yet it's also one of the oldest, most often repeated ones."

A former contributor to sites including MTV's The Backlot and Bloody-Disgusting, Chris Eggertsen worked in film development before indulging his love of pop culture writing full time. He specializes in horror, the intersection of social issues and entertainment and Howard Stern. He's on Twitter @HitFixChris.