I have read many commentaries decrying the linking of the Marvel Franchises as pure marketing. I would like to point out a few things that some seem to have missed.
One, in all of film history as far as I know there has never been a persistent world behind multiple protagonists. There have been spinoffs, but never a persistent world. The attempt to weave four franchises (Thor, Captain America, Iron Man, and The Hulk) into a single movie (The Avengers) is a historic event as far as I'm concerned. That the individual movies, excepting perhaps The Hulk, are each all successful and entertaining is to me nothing short of astonishing. I haven't seen a single movie critic mention this as the unprecedented event it is.
Two, these are comic books we're talking about here. The magic of comic books is derived from their entertainment value and their ability to convey deeper emotions, describing a spectrum for which readers will place themselves. The Hulk fundamentally is about "HULK SMASH" for entertainment and the soul searching of Bruce Banner's burden of id for the depth. Thor is about Thunder God BOOM for entertainment and the value of humility for depth. Iron Man is about Richie Rich gone badass and about human frailty and how it is masked. Captain America is about Truth, Justice, and the American Way of Smashing Evil and about being a hero by leading through example. To compare these things with Shakespeare is to compare Hamburgers with a Japanese tea ceremony; McDonalds makes burgers, and so does Gordon Ramsey, but that spectrum has no parallel in the world of traditional form. Why critics seem to bemoan the lack of elegance in a movie about a big lummox with a magic hammer is something I find perplexing.
Three, the reason comic books have crossovers is because people who love these heroes want to see them interact. Who doesn't wonder why Superman can't help Batman out sometimes? Who can't help but think while the Fantastic Four are battling Dr. Doom in the streets of Manhattan, "where's Spidey?" These characters live in the same world - it's simply common sense they would interact. I find it jarring that we'll never see Spider Man or the X-Men in this new Avengers world, thanks solely to licensing.
And finally four, we have seen a sea change in the genre of movie fantastics in the last decade or so. The day of James Bond, Flash Gordon, and 50s Superman has passed and we're now in an era where our heroes are expected to be human as well as superhuman. Being iconic is no longer enough. We are no longer looking for inspiration from our heroes, we're looking for sympathy. All of these Marvel movie franchises are feeding that need, and by crossing them with each other they are building something greater than the parts can be alone. We are seeing not just characters and story, but a world where these characters and story influence each other and as such influence us to see the connections in our own world between our own great characters and stories. As I mourn the loss of individual icons, I also celebrate the birth of something inspirational through this framework of sympathetic community. That's something special, I think.