Cinema is a form of art. And in any medium of art, those artists draw praise which innovate in their field. Those who experiment, try new things, and introduce the world to new ideas, are the ones which history remembers. The Marvel movies have done exactly that for cinema. Marvel's biggest innovation is, of course, the concept of the Cinematic Universe. They pioneered a storytelling method of making different movies with different stories focused on different characters, but all taking place in the same world. This not only gave them unique world-building capabilities, but also compounded the payoff when those story-lines finally intersected. Marvel pushes the envelope in other ways as well. By committing to hiring different, even relatively unknown directors for each of their movies, they portray different parts of their universe with different visions - from the gritty Jason Bourne-esque tone of Captain America: Winter Soldier, to the heist-crime style of Ant Man, to the improve comedy feel of Thor: Ragnarok. And by controlling technical special effects-making themselves, separate from the directors, Marvel pushed a constant quality in their effects in a way movies, especially superhero movies, didn't before. These and many other factors contribute to Marvel's staggering success. Marvel's commitment to doing new things has resulted in enormous payoff. They have found new ways to tell stories, and have pushed film-making into a wholly new paradigm. Its innovations, particularly the Cinematic Universe, has cemented it in the annals of cinema history.
The concept of the Cinematic Universe is certainly unique. But it seems to be just a nifty little trick in the grand scheme of things. A connected universe doesn't mean much if each movie piece isn't noteworthy. And given how Marvel and Disney just churn out the same surface-level action movie every year, it doesn't exactly add up to greatness. One outstanding film will be remembered more than a series of mediocre ones.