I absolutely love The Avengers (to my mind, it's probably Marvel's best film to date, perhaps excluding the first Iron Man and Winter Solider). But to me, The Avengers is a cheeseburger. A brilliantly made, extremely tasty cheeseburger, but a cheeseburger nonetheless. Well-crafted blockbuster entertainment, which never strives to be anything more.
Whereas, Nolan's Batman films (perhaps excluding The Dark Knight Returns) felt like more substantial films to me, films that had a lot more substance and artistry behind them. They were films with thematical underpinnings, films that had something to say.
I mean, what were the main themes of Guardians of the Galaxy, for example? Family is good? No, there weren't really any themes. Because it was a deliriously cheerful, thrill-seeking blockbuster. But it wasn't hugely substantial as an actual film which explores its characters in depth or engages us as an audience in any kind of creative way.
I love Marvel's films, but they've still got a long way to go before they hit the highs of the Nolan films and Spiderman 2, at least in my opinion. But at the very least, Marvel Studios has an extremely strong understanding of the source material they're continuing to adapt...unlike say, Snyder and friends as they continue to mishandle comic book property after comic book property.