As Mark Harris points out in a recent Grantland essay, sequels are no longer merely a regrettable feature of the way Hollywood operates, they're pretty much the entire business model. We're supposed to get 28 of them in 2015, or one every 13 days. And yet, there was a time when "sequel" did not automatically mean a crass cash grab by an industry fresh out of fresh ideas. The best example is a film released 40 years ago this month (on December 20, 1974), "The Godfather Par II."

True, the second "Godfather" came about not because the initial story left loose ends but because the 1972 film's gargantuan success all but demanded a second trip to the well. Indeed, Francis Ford Coppola was reluctant to return to the Corleone saga. Nonetheless, he and writer Mario Puzo found a way to add to the Mafia saga that amplified and enriched the story they told the first time. The result was a film that emulated its predecessor by winning a Best Picture Oscar, made a star out of Robert De Niro the way the first film did for Al Pacino, and earned a consensus vote among film fans as the best sequel ever made.

To be fair, some of the best sequels of recent years haven't been just extra installments added as afterthoughts but actual continuations of stories that were only partially finished after the initial chapters (think the "Harry Potter" series, the "Lord of the Rings" movies, "Kill Bill," or "The Hunger Games" films). And that's actually an encouraging sign. Along with the whole Marvel Cinematic Universe concept, it shows that Hollywood at least recognizes that there has to be a new way of thinking about sequels and how they relate to an overarching narrative and set of characters, lest audiences grow tired of movies made simply to satisfy studio stockholders.

If Hollywood is looking for ways to make sequels more satisfying, it should consider the examples in the gallery above.

best movie sequels