Image source: Nickelodeon Movies.

If you've seen the reboot of the Teenage Mutant Ninja Turtles franchise, produced by action-movie guru Michael Bay, you're far from alone. The aptly named Teenage Mutant Ninja Turtles flick grabbed last weekend's top spot at the box office by collecting $65.6 million in North American ticket sales. It was the fourth-strongest August debut in Hollywood history, according to Box Office Mojo. By the second weekend, the Megan Fox vehicle will have earned out its beefy $125 million budget.

At the end of the day, Ninja Turtles should be a decent hit for Viacom (NASDAQ:VIA), whose Paramount and Nickelodeon divisions produced and distributed the film.

But that's not really the point of this movie. A close viewing will make it clear that Ninja Turtles always was intended as a tentpole film for a much larger-scale franchise. As a one-shot summer launch, Ninja Turtles would have gone down in history as a fairly humble affair and hardly worth the effort. But as the launchpad for a revitalized Ninja Turtles brand, this picture did just about everything right.

The product itself
Let's start with the movie itself.

Teenage Mutant Ninja Turtles took a storied brand, dipped it in a bucket of Michael Bay's modern special effects, and took some care to preserve the spirit -- but not the letter -- of the canonical TMNT stories. The resulting product feels relevant in the modern cinema landscape, with a gritty patina over the shiny plastic that older fans were used to.

So there's an updated look, and the entire franchise just moved from the 1980s and 1990s into the current decade. It's done with authority and a certain confidence.

At the same time, the core of the franchise remains intact. Sure, the details of these reluctant heroes have changed, but old-school fans still feel at home. Leonardo is still the leader of the pack, Michelangelo the dorky ladies' man, Shredder the implacable menace, and Fox's April O'Neil still swings between the roles of damsel in distress and problem-solving hero in her own right.

In other words, the movie splits its focus between new audiences and die-hard fans. The TMNT brand never really went away, but this is a smart approach to kick-starting the next generation of die-hards and toy collectors.

Why wasn't this a dead end?
You'll note that I said nothing about Ninja Turtles being a masterpiece. It isn't -- and it doesn't have to be.

That's good news for Viacom, because the movie gets no respect from critics and only modest approval from audiences. Rotten Tomatoes slaps it with a meager 20% approval rating from professional critics, and a lukewarm 62% of regular viewers "liked it." The story doesn't change if you switch to IMDB's critic and user polls.

These low ratings are the reason behind the "modest hit" verdict I dropped earlier. Don't expect the movie to have legs; Ninja Turtles is running into two genre rivals in The Expendables 3 and Let's Be Cops this weekend and doesn't have the word-of-mouth momentum to bowl them over. Audience sizes will drop dramatically, and these numbers never really bounce back.

Given all of these factors, you might expect Viacom to shrug, drop the whole franchise, and go looking for another eyeball magnet in the PG-13 action genre.

But Viacom didn't do that. Instead, the studio already set a June 3, 2016, release date for the sequel.

Megan Fox and Will Arnett add some human appeal to the gallery of mutants. Source: Nickelodeon Movies.

TMNT delivered where it counts
Ninja Turtles did exactly what it was supposed to do.

Blockbusters don't happen in the dog days of summer. Last year, the American box office collected a grand total of $841 million in August ticket sales. Sales were 57% higher in July and 46% higher in June. That's no fluke, but a repeating pattern stretching back for decades. The real summer blockbuster season falls between early May and late July.

So raising this potential tentpole in August sets expectations pretty low. Ninja Turtles is a legitimate hit despite a limited lifetime value. It's a low-risk strategy that's aimed at paying dividends in future releases.

Ninja Turtles 2 grabbed some prime real estate in early June. It will have to contend with some big-ticket rivals. Captain America 3 launches in early May, and another X-Men movie hits theaters just one week before the next TMNT installment.

Watching the movie, you'll see that this was the goal all along.

There's no elaborate, creative plot -- just an updated paint-by-numbers origin story. All the key characters in the Ninja Turtles universe have now been firmly introduced, each one scoring a few up-close highlight scenes to explain what makes them special. They will need no tiresome explanation in future franchise chapters. In 2016, even newcomers to this saga will know that Splinter is the Obi-Wan mentor of this series. Donatello is the brainiac nerd, and will be expected to hack computer systems in every episode.

It's all about the sequels and action figures
Teenage Mutant Ninja Turtles, the 2014 film, was never meant to break new ground. It simply had to reestablish a brand and a franchise that had turned too young and too plastic for its intended audience. This version will sell action figures and lunch boxes again, and I wouldn't be surprised to see Viacom tap its Nickelodeon arm for a Bay-style TV series on this theme, as well.

Sequels and spin-offs can keep this rebooted brand going in a big way. It's a proven strategy with a huge potential payoff.

For example, the first film in the Twilight series made $393 million worldwide. That's very respectable and a huge hit in all respects -- but it's downright forgettable next to the string of four sequels grossing at least $700 million each.

Or, perhaps closer to the Ninja Turtles reboot effort, consider Christopher Nolan's Batman films.

Batman Begins collected $372 million in global box-office dollars. More important, it set up Nolan's vision for the troubled hero and his world. Both of the sequels, The Dark Knight and The Dark Knight Rises, passed the billion dollar mark.

Ninja Turtles, before applying the Michael Bay patina. Source: Nickelodeon.

Even closer to the mark, Paramount and Michael Bay kick-started the cheesy Transformers brand with a fantastic $710 million effort in 2007. Again, all of that film's sequels have outgrossed the story primer, and the last two chapters passed the billion-dollar global level as well.

I'm not saying that the Ninja Turtles reboot will add billions to Viacom's top line in any particular year. The turtles could never quite match Batman's brooding allure, and they were always a bit more niche than Transformers. And both of those story worlds come with far richer opportunities for spin-offs and elaboration.

But the Turtles brand already comes with decades-long staying power, and this is the perfect way to keep audiences on the hook. In the long run, Viacom will enjoy the fruits of this seemingly forgettable labor.

Viacom and Michael Bay didn't exactly bring their "A" game to this film, and they really didn't have to. We should expect a stronger script and more exciting talent lineup for the 2016 sequel, which is where the franchise truly gets to test its mettle.