Even though the Marvel Cinematic Universe was already six years old at the time, Guardians of the Galaxy was a game-changer for the franchise. Taking the risk of spotlighting extremely obscure characters paid off for the studio because it became one of the biggest critical and commercial hits of 2014. With success like that, green-lighting a sequel was a no-brainer, but Marvel Studios president Kevin Feige has revealed that Guardians of the Galaxy's performance also paved the way for the MCU take more creative risks with their movies to make them feel more comic book-y. He explained:
...but certainly the success of Guardians just boosted our confidence to continue to go in new, fun, weird directions, and I think that led to Doctor Strange and certainly, ultimately, leads to the things we're doing in Infinity War. You know we did the comic books as you well know do all sorts of fun, mind-bending, trippy storylines that you really hadn't seen in any movies until we started scratching that surface with Thor and a little bit more in Avengers. A little bit in the quantum realm of Ant-Man.
After clarifying that Thor: Ragnarok would have a unique tone as opposed to just replicating what Guardians of the Galaxy did, Kevin Feige addressed how the MCU's 2014 space adventure opened the door for these movies to be weirder and more "trippy." While the MCU had already explored cosmic Marvel elements with the two Thor movies and The Avengers, Guardians of the Galaxy took focus on the crazy space content to the next level. From there, movies like Ant-Man and Doctor Strange used other dimensions/realities to their advantage, which may play a role in Avengers: Infinity War.
Now that moviegoers have shown with their dollars that these kind of comic book movies are appealing, Marvel isn't holding back on having their MCU entries be more unusual. As Kevin Feige told Heroic Hollywood:
It was really Guardians and then Strange and now Guardians 2 which is saying, 'Okay, the audience is gonna stay with us on this.' Why even attempt to make a movie out of the infinity gauntlet if you can't really do a lot of the crazy things that happen in that Jim Starlin imagination.
Marvel will take the weirdness to its highest level yet next year with Avengers: Infinity War, which will see the Avengers, Guardians of the Galaxy and more battling Thanos. And then there's Avengers 4 to consider the year after. Regardless, without Guardians of the Galaxy, it certainly would have been significantly harder to set the stage for these events.