The Marvel Cinematic Universe has managed something truly spectacular, completely redefining what Hollywood means by "franchise." There aren't just 3 Iron Man movies and 2 Captain America movies and 2 Thor movies - there are 10 interconnected movies, all living within a singular universe, chock full of references and crossovers with one another.
This has been going on since Iron Man was released in 2008, and is due to continue indefinitely. Phase 1 comprised of Iron Man 1 & 2, The Incredible Hulk, Thor, and Captain America - and finally culminating with the biggest crossover in cinematic history, The Avengers.
With that, Marvel entered a less-certain Phase 2 - trying to replicate and continue the success of Phase 1, and miraculously somehow pulled it off. Iron Man 3, Thor 2, Captain America: The Winter Soldier, and now Guardians of the Galaxy have all been top-notch superhero films, and there seems like little doubt that Avengers: Age of Ultron will knock it out of the park.
This was the impossible dream of every comic book geek back in the 90s. Now it's reality. Pretty cool, huh?