When the first "Guardians of the Galaxy" came out in 2014, it was a surprise box office hit, considering how few members of the mass audience were familiar with the space epic's characters.

Fast forward to 2017, and "Guardians of the Galaxy Vol. 2." is an even bigger smash -- but not as big as many had predicted.

"Guardians Vol. 2" opened this weekend with an estimated $145.0 million, making it the sixth-biggest May debut ever, and yet that number almost seems like a disappointment. Yeah, it sounds petty to grumble about such a huge figure, but then, experts had been predicting an opening at $150 -- at one point, predictions were as high as $160 million or even higher.

Should "Guardians 2" have opened bigger? It certainly did better than the debuts of such Marvel sequels as "Iron Man 2," "Captain America: The Winter Soldier," and "Thor: The Dark World." Its 54 percent increase over the opening weekend of the first "Guardians" is the biggest percentage jump for any second film in a Marvel Cinematic Universe series.

Still, its failure to meet its projections may make you wonder: Are the new standards of Hollywood's all-blockbusters-all-the-time business model out of whack? Or is something else going on regarding the ticket buyers that Hollywood does -- and does not -- target?

Guardians Of The Galaxy Vol. 2..Star-Lord/Peter Quill (Chris Pratt)..Ph: Film Frame..©Marvel Studios 2017For some perspective, it's worth looking at what "Guardians 2" had going for it, and what its weaknesses were.

On the plus side, there's the Marvel name. Arguably, it was the brand that helped make a sleeper hit out of the first "Guardians" three summers ago. Few experts had predicted that a superhero saga featuring largely unfamiliar characters -- including an angry raccoon and a talking tree -- would have been a smash. But the goodwill that Marvel has earned over the years carried a lot weight and allowed a lot of viewers to give the film the benefit of the doubt. Not only did the movie open with an astonishing $94.3 million, but it went on to gross $333 million in North America and $773 million worldwide.

True, the first "Guardians" wouldn't have earned those kinds of numbers if not for positive word-of-mouth once the film opened, but the Marvel name is what kicked the door open. "There's a general halo of quality with the Marvel brand," as Dave Hollis, Disney's Executive Vice President for Theatrical Distribution, put it in an interview with Moviefone.

Now that "Guardians" is an established franchise, however, the sequel is playing a different, more traditional game. Its position as the first blockbuster of the summer follows a carefully-drawn, time-tested blueprint. After all, movies featuring Marvel characters have owned the summer-kickoff slot for the past decade; Marvel films have kicked off the first weekend in May every year since 2007. (Only 2007's "Spider-Man 3" isn't from the Marvel Cinematic Universe, but obviously features a Marvel hero.)

All five of the May movies that have opened bigger than "Guardians 2" are Marvel movies from the first weekend of the summer, and four come from the past five years. Still, why couldn't "Guardians 2" open bigger than a movie from 10 years ago, the least-loved of the three Tobey Maguire "Spider-Man" films?

"Guardians 2" opened on 4,347 screens, a number that's on a par with "The Avengers" (whose $207.4 million debut on the first weekend of May in 2012 is the best opening ever for Marvel and the third biggest opening weekend in history). That represents about 100 more screens than "Spider-Man 3" (which premiered with $151.1 million) or "Iron Man 2" (opening with $128.1 million on this weekend in 2010). It helped "Guardians" that almost all its screens were premium-format theaters that charge audiences extra. There were some 3,800 3D screens, 388 IMAX screens, 588 large-format screens, and 194 theaters with jostling D-Box seats. The IMAX screens alone yielded $13 million toward that $145 million debut.

Still, while a lot of the film's reported $200 million budget went toward visual spectacle, the movie's key source of appeal, outside of the characters, may have been nostalgia. There's the much-anticipated soundtrack of vintage '70s pop tunes, which was playing in rotation all weekend on Sirius XM's '70s station. There's also the key roles for old-school action-movie stalwarts Kurt Russell and Sylvester Stallone. Indeed, looking at the media coverage of "Guardians 2" over the last week, you'd have thought Russell was the star, not Chris Pratt.

The result was an audience that was largely older. Only 28 percent of the audience consisted of families or teens, and only 40 percent of the viewers were under 25.

There are two dangers here. One is the conventional wisdom that it's younger viewers that drive the box office, particularly for comic-book movies. The other is that the older audience still relies on reviews, which were less than enthusiastic; apparently, critics who enjoyed the novelty of the first "Guardians" felt that the sequel was just more of the same -- if not less at times.

Hollis said that the absence of novelty was less of a liability than a creative opportunity. "When you have a sequel to a film that broke out the way the first 'Guardians' did," according to Hollis, "you no longer have the element of surprise, but what you gain is the audience's affection, which gives you the luxury to really delve into the world and the many unique and compelling things, from the colorful characters and the pitch-perfect cast to the music and visuals, that set it apart."

Indeed, word-of-mouth among paying customers was stronger than the reviews -- the movie earned a solid A at CinemaScore, Marvel's tenth consecutive film to do so -- but Disney had to get those viewers into theaters first.

Did Disney write off the kind of younger, mainstream viewers who usually make these films into hits? Not exactly. You don't get to $145 million without marketing aggressively to young and old alike. The challenge is to sell each of these films with what Hollis calls "event-level marketing that feels personal." For "Guardians 2," that meant making the adorable Baby Groot ubiquitous, appearing everywhere from "SportsCenter" (on Disney-owned ESPN) to Go-Gurt ads, prompting massive viral sharing of images and video of the lovable shrub.

Still, the usual blockbuster crowd was not Disney's highest priority this time. That was the overseas audience, most of whom got to see "Guardians 2" a week before Americans did. The movie has already earned $282.6 million abroad, nearly twice what it's made here, for a worldwide total of $427.6 million. So "Guardians 2" is well on its way toward a $1 billion global gross. Forget the domestic earnings; international is the new benchmark for success. Anything less than a billion -- like the $773 million worldwide gross that the first "Guardians" earned three years ago -- could now be seen as a disappointment.

"Guardians Vol. 2" is the latest of several big-budget Hollywood launches this year, from "Beauty and the Beast" to "The Fate of the Furious," that was made with someone other than the domestic, English-speaking audience in mind.

It's a vast movie galaxy out there. Domestic audiences who spent $145 million to watch the multi-racial, multi-species "Guardians 2" may soon realize that they're just a small part of it.