Movie franchises have existed for decades; go back to the 30s and 40s and you'll find low-rent (often comedy) franchises with a dozen entries, if not more. Those series operated most often in the same way sitcoms do - a situation and characters are established up front and then comedy ensues in each entry. There wasn't a huge throughline, although later entries would assume you knew who everybody onscreen was. Serialized franchises have existed for a while (I still believe that Planet of the Apes is the greatest serialized franchise of all time because of its bizarre continuity), but over the last few years they have really become the norm. There are still franchises that just roll from instalment to instalment - see the Die Hard movies - but studios tend to now think in terms of planned trilogies with long arcs. The Harry Potter movies are the ultimate example of the modern serialized franchise - it's one story continued over eight films that, by the middle, becomes impenetrable to outsiders. You could (if you hated yourself) just watch Live Free or Die Hard and 'get it.' Good luck jumping in at Harry Potter and the Deathly Hallows Part 1.
Now Marvel Studios is pushing the evolution of franchise films to another level. They're going beyond the idea of a serialized story contained in a single franchise and they're spreading their story out through all of their series, basically making the Marvel Studios films one big franchise that has two movies open a year. "No duh," you say. "This has been apparent since they announced The Avengers."
Well, yes. Sort of. Until Phase Two began it seemed plausible that the individual franchises would bump against each other every three years in another Avengers movie, and that you could happily ignore the rest of the films, but Iron Man 3 and Thor: The Dark World show that perhaps the studio is playing it very differently, and I suspect that by the time we get to Phase Three you're going to have to watch every single movie Marvel releases to keep up.
Iron Man 3 and Thor: The Dark World are both direct sequels to The Avengers. In Iron Man 3 Tony's personal conflict stems directly from The Avengers - if you didn't see that movie you didn't have the background on his mental state (it is, of course, basically filled in for those who missed the second biggest movie ever or who forgot). Thor: The Dark World opens with Loki returning in chains to Asgard, a very different status quo than where we left Loki at the end of Thor. You could simply watch the Thor movies all in a row, but that's not the best - or intended experience.
I can't think of another franchise that has done this. You can watch the Indiana Jones movies without having to worry about seeing any other film in any other franchise. Right now it's a small thing - there are details and character bits in Thor: The Dark World that work because you've seen The Avengers - but the Thor: The Dark World end credits sequence indicates we're about to see everything get much more tied together.
Slight, minor, and vague spoilers follow.
In the first of two credits stings, it is revealed that the Marvel Cinematic Universe has already introduced two of the six Infinity Gems, powerful items that, in the comics, allow their owner to control all of the universe - to become, essentially, God. It's now clear that this is all building up to The Avengers 3, which will have Thanos obtain the Gems and wreak havoc, as he did in the famous Infinity Gauntlet miniseries, a defining Marvel Comics event. It's also clear that the remaining four gems will show up in different Marvel movies over the course of the next few years, and will all have been revealed by The Avengers 3, if not actually all collected by Thanos by then.
That's an actual narrative throughline that will connect the films by more than just crossover; there is an overarching storyline that will reach through all of the movies (interestingly only the Iron Man movies will be outside of that overarching plot - The Incredible Hulk as well, although I guess we're forgetting that one exists). By the time Phase Three begins the Marvel Cinematic Universe won't just be a series of movies that are sitting next to each other, occasionally rubbing elbow, they're going to be a single long franchise telling one story leading up to one conclusion in The Avengers 3.
It's insanely ambitious, and it's all based on brand recognition. Marvel Studios is jockeying to be Pixar - the studio whose movies you go see because they come from this particular studio - but with the added layer of creating one long narrative. Imagine if all the Pixar movies weaved in and out and you'd still have a less complex situation than a studio that releases two movies a year and uses them all to create an actual chaptered narrative. Marvel Studios is truly bringing comic book storytelling to the big screen in a way that no one ever imagined possible. I do think Marvel Studios will avoid the pitfall into which comics have fallen - the intertwined narratives between comic series are so closely connected you cannot follow the story without reading all the titles - but I think they're going to get as close to that as they can. They're going to begin making all of their individual series sequels to The Avengers movies as opposed to simply standalone concepts.
Of course every other studio sees what Marvel is doing and misunderstands it. Yes, the crossover and interwoven narrative of the Marvel Cinematic Universe is incredibly exciting and interesting and unique, but it's the characters that make it work. There's a cameo in Thor: The Dark World that works not because of continuity or the long arc leading to The Avengers 3 but because we like these characters; it's fun to see them pop up again. Warner Bros is creating Batman vs Superman, a movie that has a new Batman going up against a very undefined new Superman that uses crossovermania as its launching point. They don't seem to understand that the best scene in The Avengers isn't an action bit or a mythology moment - it's the end gag of the characters eating shawarma together. That moment defines the appeal of the Marvel Cinematic Universe more than any other - these are good, strong characters well portrayed and we like seeing them hanging out.
Batman vs Superman isn't the only thing coming from the success of Marvel's non-linear franchise strategy. The new Star Wars movie scenario - a connected trilogy with standalone movies in between each - is one hundred percent influenced by what Marvel has done. Marvel has brought us into a post-title franchise age; the brand identity is the franchise driver, not the individual movies. You may not get every viewer of Episode VII to see Young Yoda Chronicles, but you'll get enough, just as you'll get enough people who saw The Avengers to come see each individual Marvel movie. And over time, as Marvel pulls those elements closer together, they'll grow the audience for each individual series.
Ten years ago I was telling readers there would never be a cinematic universe that combined characters the way comic book universes do. Then Marvel Studios came along and proved me wrong. When it became clear that the studio was building towards a crossover, I said that there was no way they would link the individual franchises together so closely that each needed to each be watched in order, but I suspect that in Marvel Phase Three I'm about to be proven way wrong again. Just as everybody else is picking up on the idea of expanded, crossover-heavy universes, I think Marvel is about to pull it all together in the biggest way possible.